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Acromegaly is a chronic, debilitating condition caused by excessive secretion of growth hormone (GH). In the majority of cases the condition results from benign pituitary adenomas or, rarely, from ectopic production of GH-releasing hormone. Regardless of the cause, excess GH results in physical disfigurement associated with arthropathy, diabetes, hypertension, cardiac dysfunction, obstructive sleep apnea and colonic neoplasia. The death rate for acromegalic patients is 2 to 3 times higher than that of the general population, but with appropriate reduction of GH hypersecretion it tends to shift into the normal range. Treatment is thus aimed at normalizing GH secretion; eradicating or stabilizing the pituitary tumour while preserving normal pituitary function, and managing the associated complications. The treatment modalities available to achieve these objectives include transsphenoidal surgery, pharmacotherapy and radiation, or various combinations of these. This review provides an update on our current understanding of the pathophysiology of GH hypersecretion in acromegaly, the newly defined diagnostic criteria and the end point for a cure for acromegaly, and on new developments in drug treatment with the advent of slow-release forms of somatostatin analogues and the longer-acting dopamine receptor agonists, as well as in the area of radiotherapy. Its main purpose is to guide any physician involved in the diagnosis and management of patients with acromegaly.

Utilizing VIP and five VIP analogues, concentration-response curves for relaxation of rat mesenteric artery and rat gastric longitudinal muscle were determined for comparison with our previously published radioligand binding data on rat smooth muscle and other tissues. The biological potency of the VIP analogues in the present study compared more closely with their potency for VIP receptor binding in smooth muscle tissue (arteries) vs. other tissues (pituitary, brain, liver).

The pharmacological properties of the pituitary adenylate cyclase activating peptides (PACAPs) and vasoactive intestinal peptide (VIP) were compared using: (i) relaxation of vascular and gastric smooth muscle in vitro, and (ii) radioligand binding to membrane preparations of a variety of tissues. Vasoactive intestinal peptide and PACAP-27 were similarly potent in relaxing rat mesenteric arteries, porcine coronary arteries, and rat gastric smooth muscle, whereas PACAP-38 was either more or less potent than the other two peptides depending on the tissue model. Cross-desensitization to relaxation and radioligand binding studies of porcine coronary arteries suggested that VIP and the PACAPs interact with a common receptor in this tissue. A PACAP-preferring receptor with low affinity for VIP was identified in radioligand binding studies of rat brain and anterior pituitary. A second, nonselective, receptor that binds VIP and both PACAPs with high affinity was observed in preparations of rat and porcine arteries and rat lung, liver, brain, and anterior pituitary.

Whether somatostatin causes endothelium-dependent contraction (EDC) in isolated canine basilar arteries was examined. Somatostatin (10(-8)-10(-6) M) caused transient contractions in a dose-dependent manner. These contractions were abolished by removal of the endothelium, while the contractile response to neuropeptide Y occurred even after removal of the endothelium. The EDC induced by somatostatin (10(-7) M) was affected by neither atropine (10(-6) M) nor cyclo-somatostatin (10(-5) M), which suggests that the EDC is not due to release of endogenous acetylcholine and that the endothelial somatostatin receptor is different from hormonal somatostatin receptors. The somatostatin-induced EDC was attenuated by cyclooxygenase inhibitors (aspirin and indomethacin), thromboxane A2 (TXA2) synthetase inhibitors (OKY-064 and RS-5186), and TXA2 antagonists (ONO-3708 and S-145), which suggests that the endothelium-derived contracting factor is TXA2. These findings demonstrate that somatostatin causes EDC via activation of TXA2 synthesis in canine cerebral arteries.

We investigated the effect of surgical castration of male rats on the binding of [Tyr(125I)10]VIP to receptors on the anterior pituitary gland, superior mesenteric artery, brain, liver, and prostate gland. In anterior pituitary membranes the maximum number of VIP binding sites was increased whereas binding affinity was decreased 24 hours following castration. In particular, the high affinity equilibrium dissociation constant (KD) increased from 0.13 +/- 0.02 nM (mean +/- SEM) to 0.67 +/- 0.07 nM and the maximum number of high affinity binding sites (Bmax) increased from 71 +/- 9 to 470 +/- 112 fmol/mg protein. No significant change was observed in the other tissues. Anesthesia or sham operation did not alter the anterior pituitary VIP receptor binding parameters. The changes in the VIP receptor 24 hours after castration were prevented by prior injection of testosterone. These findings demonstrate tissue-selective alterations to the anterior pituitary VIP receptor by castration that are likely mediated by withdrawal of testosterone.

Vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are homologous neuropeptides with parallel biological actions. These similarities raise the question whether VIP and PHI have common or distinct mechanisms of action, including receptors. The present study attempted to distinguish specific binding sites for VIP and PHI in normal rat tissues using the homologous radioligands [Tyr(125I)10]VIP and [Tyr(125I)10]rat PHI. In rat brain, anterior pituitary, and liver membranes both radioligands identified a VIP-preferring receptor. Rat PHI had less than 10% the binding potency of VIP in these tissues irrespective of which radioligand was used. In rat uterine membranes [Tyr(125I)10]VIP bound to a receptor with approximately 100 times greater affinity for VIP over PHI. No specific binding of [Tyr(125I)10]rat PHI to rat uterus could be demonstrated. In conclusion, these results support the predominance of VIP-preferring receptors as opposed to PHI-preferring receptors in normal rat brain, anterior pituitary, liver and uterus.

The regulation of female rat anterior pituitary vasoactive intestinal peptide (VIP) receptors was examined during postnatal development and lactation. VIP receptor binding to anterior pituitary membranes from 1- to 60-week-old rats and lactating rats was examined using HPLC purified [Tyr(125I)10]VIP. Nonlinear regression of competitive binding studies indicated the presence of 2 VIP binding sites in 3-week and older animals, whereas only 1 site was identified in 1- and 2-week-old rats. The single site did not differ significantly in affinity or number when compared to the low affinity site of older animals. The guanine nucleotide, GTP-gamma-S, decreased the specific binding of VIP by 60-80% in 3-week and older animals, but not in younger animals. Compared with adult nonlactating animals, the number of high affinity binding sites decreased significantly during lactation, with no change in receptor binding affinity.

The relaxant action of vasoactive intestinal peptide (VIP) was investigated using helical strips of four major branches of bovine coronary arteries. The concentration of VIP causing 50 percent of maximal relaxation ranged from 23 to 90 nM. Preincubation of arterial strips with VIP shifted the concentration-response curves for contractions elicited by potassium chloride or prostaglandin F2 alpha to the right. The relaxant effect of VIP was retained following removal of the vascular endothelium or in the absence of extracellular calcium. The structurally homologous peptides porcine and human peptide histidine isoleucine (PHI) were less potent than was VIP. It is concluded that there are functional receptors for VIP in bovine coronary arteries.

The structure-activity relationships for vasoactive intestinal peptide (VIP) receptor binding were studied using N-terminally modified VIP analogs. VIP fragments, and VIP receptor antagonists. Tissue sources included bovine coronary artery, rat mesenteric artery, rat pituitary, rat brain synaptosomes, and rat liver. Experimental conditions for receptor binding were maintained as near to identical as possible. The competitive binding curves for VIP analogs were similar in the bovine and rat vascular preparations. However, appreciable differences were observed between the vascular and other preparations. The vascular receptors discriminated between [D-His1]VIP and [Phe1]VIP, whereas the receptors in other tissues did not. The greatest selectivity was found for [D-Ala4]VIP, which was among the lowest affinity analogs tested on the vasculature but among the highest affinity analogs in the other preparations. The rank orders of analog potencies were comparable for the rat brain and pituitary receptors. The rat liver VIP receptor differed from its counterpart in brain and pituitary predominantly by discriminating between [D-Phe2]VIP and [D-Arg2]VIP. The two VIP receptor antagonists bound weakly and nonselectively to all receptor preparations. Integrity of the full VIP molecule was necessary for full potency of binding to the vascular receptor. We conclude that the vascular VIP receptor possesses recognition properties that are distinct from those for VIP receptors in liver, pituitary, or brain.

Vasoactive intestinal peptide (VIP) has been implicated as a physiological PRL-releasing factor; however, characterization of VIP receptors on normal pituitaries using radioligand-binding methods has been problematic. In this study we demonstrated specific receptors for VIP in anterior pituitary glands of female rats using HPLC-purified monoiodinated [Tyr(125I)10]VIP. Binding of VIP was reversible, saturable to receptor and radioligand, regulated by guanine nucleotides, and dependent on time and temperature. Scatchard analysis of competitive binding studies indicated high and low affinity binding sites, with equilibrium dissociation constants (Kd) of 0.19 +/- 0.03 and 28 +/- 16 nM, respectively. The corresponding maximum numbers of binding sites were 158 +/- 34 fmol/mg and 11.7 +/- 6.9 pmol/mg. Binding was specific, as peptides with structural homology to VIP were less than 100th as potent as VIP. The rank order of potency of the peptides tested was VIP greater than rat (r) peptide histidine isoleucine = human (h) PHI greater than rGRF greater than bovine GRF = porcine PHI = VIP-(10-28) greater than hGRF greater than secretin greater than apamin greater than glucagon. Radioligand binding was associated primarily with lactotrope-enriched fractions prepared by unit gravity sedimentation of dispersed anterior pituitary cells. VIP stimulated PRL release from cultured rat anterior pituitary cells, with an ED50 of 1 nM. These results, comprising the first identification of specific VIP receptors in normal rat anterior pituitary tissue using radioligand-binding methods, provide additional support for a biological role of VIP in lactotrope function.

Adenylate cyclase in microvessels isolated from rat cerebral cortex was stimulated by guanine nucleotides, catecholamines, prostaglandin E1, prostaglandin E2, and 2-chloroadenosine. Catecholamine stimulation was mediated by interaction with beta-adrenergic receptors. The order of relative potency was: isoproterenol greater than epinephrine greater than norepinephrine. Activation of microvessel adenylate cyclase by prostaglandins E1 and E2 as well as by 2-chloroadenosine was dose related. Twenty-two peptides were tested for possible effects on the microvessel adenylate cyclase. Only vasoactive intestinal polypeptide (VIP) was stimulatory. No inhibitory action was observed. Activation by VIP required guanosine triphosphate and was dose dependent from 10 nM to 1 microM (ED50 = 0.1 microM). At 30 degrees C, stimulation of adenylate cyclase by the peptide increased linearly with time for up to 15 min. The effect of VIP was not inhibited by phentolamine or propranolol, suggesting that its action was not elicited by interaction with alpha- or beta-adrenergic receptors. Activation achieved by VIP and isoproterenol, prostaglandin E1, or 2-chloroadenosine was the sum of the individual stimulations, suggesting that receptors for VIP were distinct from those for isoproterenol, prostaglandin E1, and 2-chloroadenosine.

Somatostatin-like immunoreactivity was detected by a specific radioimmunoassay in extracts of retinas of Dutch-belted rabbits at a mean concentration of 1.1 +/- 0.1 ng/retina, or 170 +/- 30 pg/mg protein. On both gel permeation chromatography and reversed phase high performance liquid chromatography, the majority of this material was indistinguishable from somatostatin-14; a smaller amount of immunoreactive material co-chromatographed with somatostatin-28. The somatostatin-like immunoreactivity was concentrated in a P2 (synaptosomal) fraction prepared by differential centrifugation. The concentration of somatostatin-like immunoreactivity was unaffected by the prior intravitreal injection of the selective neurotoxins 6-hydroxydopamine and 5, 7-dihydroxytryptamine. The rabbit retina, therefore, contains readily detectable amounts of material chemically similar to somatostatin-14 and somatostatin-28. This material is concentrated in neurosecretory elements of the retina, but is not contained in cells which accumulate dopamine or indoleamines. The rabbit retina is suitable for in vitro studies of the central nervous system function of the somatostatin family of peptides.

The purpose of this investigation was to 1) develop a hypothalamic perifusion system which would allow measurement of spontaneous basal somatostatin (SRIF) release, 2) compare the immunological and biological activities of released SRIF, and 3) study the effect of membrane depolarization, extracellular calcium, and several neurotransmitters on SRIF release. Release was greater at the beginning of the perifusion and decayed with time for 90 min, after which it stabilized and remained constant for 3 h, the period used to determine the mean rates of release. Basal release was 20.2 pg/fragment x 10 min. Membrane depolarization with 55 mK K+ increased SRIF release 30 to 4-fold in a calcium-dependent manner. The immunoreactivity and biological activity of SRIF concentrated by affinity chromatography of hypothalamic perifusates were compared to those of synthetic SRIF and rat hypothalamic extract. Biological activity was assessed by the inhibition of radioimmunoassayable rat GH released from cultured dispersed rat anterior pituitary cells. Hypothalamic fragments were exposed to several neurotransmitters as well as other substances known to influence rat GH secretion. Our results may be summarized as follows. 1) The perifused medial basal hypothalamus releases immunoactive and bioactive SRIF at a constant basal rate. 2) Membrane depolarization with high potassium stimulates a small releasable pool of SRIF in a calcium-dependent manner. 3) Affinity chromatography is an alternative technique to collect and concentrate SRIF released from tissues. 4) Common neurotransmitter agents did not modify SRIF release from the medial basal hypothalami under the present conditions.

Somatostatin (SRIF) is a hypothalamic tetradecapeptide which acts on several different types of pituitary cells to inhibit hormone release both in vivo and in vitro. We have previously shown that the GH4C1 clonal strain of rat pituitary tumor cells contains a single class of specific high-affinity SRIF receptors and that SRIF is a potent inhibitor of GH and PRL release by these cells. In this study, we have determined the relationship between the apparent binding affinity and biological potency of 19 SRIF analogs in GH4C1 cells. Receptor binding and biological activity were assayed under identical conditions. A good correlation (r = 0.96) was observed over a 10,000-fold range between the receptor binding affinities and biological potencies of SRIF analogs. Modifications at the C- and N-terminal regions of the SRIF molecule had minimal effects on binding to the receptor or potency to inhibit PRL release. However, substitution of residues 6 through 10 or reduction of the disulfide bond resulted in a 100-fold or greater decrease in both activities. The N-terminal extended SRIF analogs, SRIF-28, [D-Trp22]SRIF-28, and SRIF-25, were all somewhat less potent than SRIF. These results strongly support the involvement of the characterized SRIF receptor in initiating the biological actions of SRIF in GH4C1 cells and define the structural features of the SRIF molecule required for both receptor binding and activation.

A substantial body of published evidence indicates that vasoactive intestinal peptide (VIP) may function as a vasodilatory neurotransmitter to cerebral blood vessels via a specific VIP receptor. In the present study in vitro autoradiography utilizing monoiodinated [125I-Tyr10]-VIP demonstrated VIP binding sites in the medial layer of bovine anterior, middle, and posterior cerebral arteries. This observation is consistent with the VIP receptor being localized in vascular smooth muscle components.

We have studied the vasorelaxant properties of vasoactive intestinal peptide (VIP) using helical strips of bovine, porcine and human brain arteries in vitro. The resting tension of the arterial strips was increased during experiments by prostaglandin F2 alpha or KCl so as to increase the magnitude of the relaxant response to VIP. Arteries supplying different regions of the bovine brain responded potently to VIP with ED50 values of 1.8 nM, 2.3 nM, 6.8 nM and 9.0 nM for the middle, anterior and posterior cerebral arteries and the basilar artery, respectively. The porcine basilar artery and branches of the human middle cerebral artery responded to VIP with ED50 values of 4.2 nM and 1.6 nM, respectively. The homologous neuropeptide, PHI, relaxed the bovine middle cerebral and porcine basilar arteries less potently than did VIP, with ED50 values for PHI being 11 nM and 43 nM, respectively. However, PHI elicited in the two arteries a maximal vasodilatory response of similar magnitude as did VIP. The other homologous peptides, human pancreatic growth hormone releasing factor 1-40 [hpGRF 1-40], secretin, and glucagon, and the VIP fragments, VIP 1-12 and VIP 10-28, were completely inactive. In contrast, VIP, which had been oxidized to VIP-(Met17 sulfoxide) or VIP-(Met17 sulfone), retained full activity. These structure-activity relationships for relaxation of brain arteries are consistent with previous studies of other biological responses to VIP.

A 20-year-old man died from Aspergillus pneumonia three weeks after heavy exposure to grain dust. Lung biopsy and autopsy demonstrated a distinctive form of suppurating granulomatous bronchopneumonia caused by Aspergillus fumigatus, which was the sole agent cultured from the tissue. The liver and lymph nodes contained pigmented lipid histiocytes characteristic of chronic granulomatous disease, and subsequently both of the patient's brothers were found to have X-linked chronic granulomatous disease. The authors suggest that this morphologic expression of Aspergillus pneumonia should raise a suspicion of neutrophil dysfunction or chronic granulomatous disease.

We have studied the effect of parathyroid hormone (PTH) on adenylate cyclase of microvessels isolated from rat cerebral cortex. Native bovine (b) PTH-(1-84), the synthetic amino-terminal fragment bPTH-(1-34) and the synthetic analog [Nle8,Nle18,Tyr34]-bPTH- (1-34) amide stimulated adenylate cyclase in a dose-dependent manner with apparent ED50 values of 16 nM, 6.3 nM and 15 nM respectively. The stimulation by bPTH was greatly enhanced by guanosine triphosphate. The PTH antagonist, [Nle8,Nle18,Tyr34]-bPTH-(3-34) amide inhibited the action of bPTH-(1-84) and bPTH-(1-34). In summary, PTH stimulated adenylate cyclase in rat cerebral microvessels in a very similar manner to its stimulation in the renal cortex.

The regions of the somatostatin (SRIF) molecule recognized by five antisera were systematically studied using three radioligands (125I-N-Tyr-SRIF, [125I-Tyr1]-SRIF and [125I-Tyr11]- SRIF) and SRIF analogs containing sequential substitutions with alanine or tyrosine. Antisera SA and moreso SB had N-terminal specificity when used with [125 I-Tyr11]-SRIF but central molecular specificity when studied with the two N-terminal radiolabelled analogs. The N-terminal and central specific populations of antibodies in antiserum SB were separable by immunoaffinity adsorption using immobilized [Tyr1]-SRIF. It is of practical significance that the same antiserum (SB) could be used with different radioligands to perform N-terminal and central specific radioimmunoassays (RIAs). The central specific RIA detected SRIF-14 and SRIF-28 on an approximately equimolar basis whereas the N-terminal specific RIA was selective for SRIF-14.

The regional distribution of somatostatin-, substance P- and neurotensin-like immunoreactivity was determined in 41 areas of 10 human brains. Each peptide is distributed widely in the human central nervous system and for each the pattern of distribution is unique. No significant relationship was found between peptide levels and patient age, interval between death and autopsy, and tissue storage time prior to assay. The regional distribution of these peptides is similar to that seen in several animal species and the pattern of this distribution is consistent with the idea that peptides function as neurotransmitters within the central nervous system. The problems of using human post-mortem material for peptide assay are discussed.

Analysis of somatostatin-like immunoreactivity (SLI) in guinea pig brain by HPLC and radioimmunoassay revealed an unexpected peak of SLI eluting at a retention time slightly later than standard somatostatin-14. The following evidence argues that this peak represents dihydro (H2) somatostatin-14. (1) The peak had the same retention time as standard [H2]somatostatin. (2) The possibility of a reduction artefact due to tissue processing was excluded by adding exogenous somatostatin-14 or 125I-labeled N-Tyr-somatostatin-14 to tissue and observing that no corresponding reduced peptides were generated. (3) Mild oxidation of brain extracts with H2O2 decreased, whereas mild reduction with dithiothreitol increased, the proposed peak of [H2]somatostatin. (4) Reaction of tissue extracts with iodoacetamide decreased the size of the proposed [H2]somatostatin peak but resulted in generation of a new peak co-eluting with standard carboxymethylated somatostatin-14. The proportion of the [H2]somatostatin peak in five brain regions, the hypothalamus, amygdala, cerebral cortex, brainstem and cerebellum, ranged from 6 to 20% of total SLI. The probability of somatostatin-14 existing endogenously in reduced or oxidized forms may have implications for its biological function in the guinea pig.

This study reports the characterization of receptors for vasoactive intestinal peptide (VIP) on membranes prepared from bovine cerebral arteries. By use of HPLC we prepared two purified monoiodinated VIP radioligands with nearly equivalent cerebral vasorelaxant potency as native VIP, [Tyr(125I)10 )VIP and [Tyr(125I)22]VIP. The former resulted in a higher proportion of specific binding to arterial membranes than the latter and was therefore thought to be the superior radioligand for receptor characterization. The binding of [Tyr(125I)10]VIP to cerebral arterial membranes was saturable, specific, reversible, and dependent on time and temperature. Scatchard analysis suggested the presence of a high- and a low-affinity binding site with KD values of 0.2 and 11 nM and receptor concentrations of 79 and 737 fmol/mg of protein, respectively. The dose-response curves for binding to the VIP receptor by the VIP-homologous peptides PHI, PHM, and rat growth hormone-releasing factor (GRF) were very similar to their dose-response curves for relaxation of cerebral arteries. The order of potency was VIP greater than PHM greater than PHI greater than rat GRF. It is suggested that the characteristics of the vascular VIP binding sites and the close correlation between the binding and vasorelaxant properties of VIP and its related peptides argue for the vascular binding sites being functional receptors for VIP.

We have studied the responsiveness of vascular adenylate cyclase to vasoactive intestinal peptide (VIP) and parathyroid hormone (PTH) using preparations of cerebral microvessels and arteries. Cerebral microvessels obtained from rats, guinea-pigs, cattle, and pigs all responded potently to bovine (b) PTH-(1-34), whereas considerable between-species variability was observed in the responsiveness to VIP. The homologous peptide to VIP, PHI (porcine heptacosapeptide), stimulated adenylate cyclase in both rat microvessels and a broken-cell preparation of bovine arteries. The ED50 values for activation of bovine arterial adenylate cyclase by VIP, PHI, and bPTH-(1-34) were 6.9 nM, 10 nM, and 100 nM, respectively, with the following order of efficacy: VIP = PHI greater than bPTH-(1-34). The other related peptides, hpGRF (human pancreatic growth hormone releasing factor), secretin, and glucagon, and the fragment VIP-(10-28) were inactive. The PTH antagonist, [Nle8, Nle18, Tyr34]bPTH-(3-34) amide, inhibited bPTH-(1-34) activation of vascular adenylate cyclase but did not affect activation by VIP using either microvessels or arteries. VIP or PHI demonstrated an additive effect with bPTH-(1-34) on vascular adenylate cyclase activity. However, the effects of VIP and PHI were nonadditive with each other. These data suggest that VIP and bPTH-(1-34) activate cerebral vascular adenylate cyclase by interacting with pharmacologically distinct receptors, whereas PHI and VIP likely interact with a common receptor.

The natural product, forskolin, which stimulates adenylate cyclase by a direct, non-receptor-mediated mechanism, was studied for its effect on the tension of isolated brain arteries and adenylate cyclase activity of cerebral arteries. Helical strips of bovine and porcine basilar arteries and bovine middle cerebral arteries, which had been precontracted with prostaglandin F2 alpha (PGF2 alpha) or KCl, relaxed potently to administration of forskolin with ED50 values, ranging from 22 to 69 nM. Incubation of forskolin with a broken cell preparation of bovine cerebral arteries resulted in an efficacious stimulation of adenylate cyclase, approximating 5 times basal activity at a forskolin concentration of 1 microM. The metal salts nickel chloride and manganese chloride decreased the potency of vasorelaxation by vasoactive intestinal peptide (VIP), which stimulates adenylate cyclase via the VIP receptor. In contrast, nickel chloride had little effect on vasorelaxation by forskolin. The endogenous nucleoside, adenosine, which acts via the adenosine receptor and adenylate cyclase, relaxed bovine basilar and middle cerebral arteries with ED50 values ranging from 0.26 to 0.94 microM. The data presented support a role for adenylate cyclase in mediating vasodilation of brain blood vessels.

Somatostatin-like activity, as determined by radioimmunoassay and bioassay, is present in HCl extracts of rat retina. The concentrations of immunoreactive somatostatin are 612 +/- 43 (mean +/- SEM)pg per whole retina of 0.621 +/- 0.044 pg/microgram of protein in retinas from rats killed by decapitation, values which are not significantly different from those in retinas from rats killed by ether inhalation. The immunoreactive somatostatin was partially purified and concentrated by immunoaffinity chromatography. Both the crude retinal extracts and the immunoaffinity-purified immunoreactive somatostatin inhibited, in a dose-related manner, the release of rat growth hormone from dispersed rat anterior pituitary cells in culture. When the immunoaffinity-purified immunoreactive somotostatin was subjected to gel filtration chromatography, 96% of the recovered somatostatin eluted as a peak corresponding in position to that of synthetic somatostatin. Retinas from a group of rats with hereditary degeneration of the photoreceptor cells and another group of rats studied 1 year after transection of the optic nerves demonstrated an increased concentration of immunoreactive somatostatin compared to controls.

Previous studies have demonstrated a specific vascular receptor for the neurotransmitter peptide, vasoactive intestinal peptide (VIP), and have suggested that the receptor is positively coupled to vascular adenylate cyclase. The present study addressed the questions whether the vascular VIP receptor is subject to regulation by guanine nucleotides and whether a disulfide reducing agent, dithiothreitol, would perturb the binding function of the vascular VIP receptor. Guanosine triphosphate (GTP) and its non-hydrolyzable analogs, guanylyl imidodiphosphate (Gpp(NH)p) and guanosine-5'-O-(3-thiotriphosphate) (GTP-gamma-S), increased the rate of dissociation of radiolabeled VIP from arterial receptors in a concentration-dependent manner. GTP-gamma-S increased the equilibrium dissociation constant (KD) of the high affinity vascular VIP binding site, a result consistent with decreased high affinity binding of VIP induced by GTP-gamma-S. These results are consistent with a regulatory role for guanine nucleotides in the function of the vascular VIP receptor. The disulfide reducing agent, dithiothreitol, caused a decrease in specific binding of radiolabeled VIP. Upon Scatchard analysis the effect of dithiothreitol was characterized by an increase in the KD and a decrease in the maximum number of binding sites (Bmax) of the high affinity binding site. These results suggest that disulfide bonds are important for ligand binding to vascular VIP receptors. The sulfhydryl alkylating agents, N-ethylmaleimide and iodoacetamide, had minimal effects on radioligand binding.

This study examined the utility of four polycationic agents for treating glass fibre filters used in the receptor binding assay for vasoactive intestinal peptide (VIP). Polyethylenimine (PEI), polybrene, protamine and methylated bovine serum albumin proved satisfactory in terms of low filter binding of free radioligand and retention of membrane-bound radioligand. Their performance was superior or comparable to untreated Millipore EGWP cellulose acetate filters which we had previously utilized but which are no longer manufactured. The results with polycations indicate the importance of ionic interactions between filter, biological membranes and radioligand in determining the performance of a filtration assay for radioligand-receptor binding. At a practical level, PEI has the disadvantage of potential toxicity. The satisfactory performance of the other polycations indicates that they provide safer alternatives to PEI for filtration assay of the VIP receptor and possibly receptors for other basic ligands.

We have studied the relaxant effect of bovine parathyroid hormone (bPTH) on helical strips of branches of bovine and human middle cerebral arteries and bovine and porcine basilar arteries. All arteries were studied after contraction with prostaglandin (PG) F2 alpha or KCl. In the case of all arteries contracted with PGF2 alpha, the ED50 of PTH vasorelaxation related to maximal vasorelaxation induced by papaverine ranged from 9 to 14 nM for bPTH-(1-34) and 100 to 220 ng/ml for native bPTH-(1-84). The PTH inhibitor, [Nle8, Nle18, Tyr34]bPTH-(3-34) amide, attenuated the vasorelaxant effect of both bPTH-(1-34) and bPTH-(1-84). The vasorelaxant effects of PTH which we have observed in this study are consistent with the stimulatory effects of PTH on vascular adenylate cyclase which we had previously reported.

Using a biologically active radioligand, [Tyr(125I)10]VIP, we have identified and characterized receptors for vasoactive intestinal peptide (VIP) on membranes prepared from the rat superior mesenteric artery and bovine coronary arteries. Binding was specific, saturable, reversible and dependent on time and temperature. Scatchard analysis suggested the presence of a high and a low affinity binding site in each arterial system with the following binding constants: the rat mesenteric artery, KD = 0.22 +/- 0.02 and 13.6 +/- 7.8 nM (corresponding maximum number of binding sites, RO = 606 +/- 44 fmol/mg protein and 2.1 +/- 0.2 pmol/mg protein); bovine circumflex coronary artery, KD = 0.10 +/- 0.01 and 37.8 +/- 16.1 nM (corresponding RO = 369 +/- 65 fmol/mg protein and 2.0 +/- 0.7 pmol/mg protein); bovine left and right descending coronary arteries, KD = 0.12 +/- 0.03 and 21.3 +/- 6.4 nM (corresponding RO = 472 +/- 7 fmol/mg protein and 2.2 +/- 0.3 pmol/mg protein). The arterial VIP receptors did not recognize secretin, glucagon, apamin or bovine parathyroid hormone, and had reduced affinity for PHI, PHM and growth hormone releasing factors (GRF). These recognition properties were, by and large, similar to those seen in the bovine cerebral arteries although a between-species heterogeneity of recognition function could be deduced from the differences in the competitive binding of rat and bovine vascular VIP receptors with the corresponding species-specific GRFs.

A sheep antiserum to somatostatin was used to develop RIA and immunoaffinity chromatography methods for the study of immunoreactive somatostatin (IRS) in brain tissue. IRS extracted from rat median eminence, anterior hypothalamic-preoptic area, amygdala, and parietal cortex bound reversibly to immunoaffinity columns, providing a technique for concentration and partial purification. Immunoaffinity purified IRS from each of the four brain regions eluted as four peaks on gel filtration chromatography. Each peak possessed biological activity, as determined by inhibitory effects on the release of GH from cultured rat anterior pituitary cells. No differences were detected by the methods employed between IRS from the anterior hypothalamic-preoptic area, which is rich in IRS-containing neuronal cell bodies, and that from the median eminence, where IRS is localized predominantly in nerve terminals.

The localization of the somatostatin system in the brains of Richardson's ground squirrels (Spermophilus richardsonii) and European hedgehogs (Erinaceus europaeus) was described by use of immunocytochemical methods. In addition, (i) chemically differing types of somatostatin and (ii) different activity phases of the somatostatin system during the hibernation cycle were investigated in the ground squirrel by means of high pressure liquid chromatography (HPLC) and radioimmunoassay (RIA). In both species, the hypothalamic component of the somatostatin system (periventricular nuclei, fiber projections to the median eminence) is more prominent than the widespread extrahypothalamic representation of the system displaying mainly scattered perikarya and nerve fibers. The reactivity pattern of the somatostatin system varied among hibernating, aroused, and non-hibernating animals; moreover, the interspecific differences were pronounced. The activity of the hypothalamic somatostatin system in the hibernating ground squirrel appeared to be suppressed when compared to non-hibernating controls, whereas in the hibernating hedgehog this system showed signs of increased activity in comparison to non-hibernating controls. In contrast, in the present material the extrahypothalamic components of the somatostatin system did not exhibit significant changes in their activity.