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Melanin-concentrating hormone (MCH) is a cyclic nonadecapeptide involved in the regulation of feeding behavior, which acts through a G protein-coupled receptor (SLC-1) inhibiting adenylcyclase activity. In this study, 57 analogues of MCH were investigated on the recently cloned human MCH receptor stably expressed in HEK293 cells, on both the inhibition of forskolin-stimulated cAMP production and guanosine-5'-O-(3-[(35)S]thiotriphosphate ([(35)S]- GTPgammaS) binding. The dodecapeptide MCH-(6-17) (MCH ring between Cys(7) and Cys(16), with a single extra amino acid at the N terminus (Arg(6)) and at the C terminus (Trp(17))) was found to be the minimal sequence required for a full and potent agonistic response on cAMP formation and [(35)S]- GTPgammaS binding. We Ala-scanned this dodecapeptide and found that only 3 of 8 amino acids of the ring, namely Met(8), Arg(11), and Tyr(13), were essential to elicit full and potent responses in both tests. Deletions inside the ring led either to inactivity or to poor antagonists with potencies in the micromolar range. Cys(7) and Cys(16) were substituted by Asp and Lys or one of their analogues, in an attempt to replace the disulfide bridge by an amide bond. However, those modifications were deleterious for agonistic activity. In [(35)S]- GTPgammaS binding, these compounds behaved as weak antagonists (K(B) 1-4 microm). Finally, substitution in MCH-(6-17) of 6 out of 12 amino acids by non-natural residues and concomitant replacement of the disulfide bond by an amide bond led to three compounds with potent antagonistic properties (K(B) = 0.1-0.2 microm). Exploitation of these structure-activity relationships should open the way to the design of short and stable MCH peptide antagonists.

1. Net fluid absorption and transmural potential difference were measured in the rat jejunum in vivo.

The purpose of these experiments was to determine whether, in carotid arteries obtained from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) a correlation exists between access of the angiotensin-converting enzyme (ACE) inhibitor, 3-[(5-amino-1-carboxy-1S-pentyl)amino]2,3,4,5-tetrahydro-2-oxo-3S- 1H-benzazepena-1-acetic acid (CGS 16617), to tissue sites and the corresponding responsiveness of these tissues to the contractile effect of angiotensin I (ANG I). In carotid arteries isolated from SHR and WKY, the magnitude of [14C]CGS 16617 uptake was slightly greater than the [14C]sucrose uptake (the extracellular space), and the percentages of [14C]CGS 16617 and [14C]sucrose in fast and slow desaturation components were similar. Addition of high concentrations of nonradioactive CGS 16617 (10(-5)M during uptakes or washouts of [14C]CGS 16617 did not change uptake amounts or efflux rates. The dose-response curves of contractions obtained with ANG I or ANG II as well as the dose-dependent inhibition of ANG I-induced responses in the presence of CGS 16617 were similar for carotids taken from both WKY and SHR. Responses to ANG I were restored as early as 5 min after incubation solutions containing inhibitory concentrations of CGS 16617 were removed. Similarly, normal responsiveness to the contractile effects of ANG I were observed with carotid arteries removed from SHR with decreased blood pressure and plasma ACE activity after 5 weeks exposure to CGS 16617. In contrast, however, responses to norepinephrine were decreased in carotid arteries obtained from CGS 16617-treated SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study was to define the direct intrarenal actions of the new adenosine agonist CGS 21680A (hydrochloride "A" salt of (2-[p-2-carboxyethyl)phenethylamino]5'-N-ethyl-carboxamido adenosine), which is selective for the A2 receptor. CGS 21680A was infused into the left renal artery, while simultaneously measuring blood pressure (BP) and parameters of renal function from both the left and right kidneys. At doses higher than 0.05 micrograms/kg/min, CGS 21680A appeared to leak from the circulation of the infused kidney in pharmacologically significant quantities, inasmuch as BP fell and renal blood flow was increased and renal vascular resistance decreased in the noninfused contralateral kidney. At doses of 0.025 to 0.05 micrograms/kg/min, CGS 21680A appeared localized to the renal circulation, because neither BP nor any measured parameter of contralateral renal function was altered. Intrarenal infusion of 0.025 to 0.05 micrograms/kg/min of CGS 21680A increased renal blood flow but not glomerular filtration rate leading to a fall in the filtration fraction. Urine volume and urinary sodium excretion were unaffected by selective intrarenal infusion of CGS 21680A. Plasma renin activity and renin secretion rate were also not altered significantly by intrarenal infusion of 0.05 micrograms/kg/min of CGS 21680A. In contrast plasma renin activity increased significantly in response to the intrarenal infusion of 0.075 micrograms/kg/min of CGS 21680A, a dose which leaked from the kidney and lowered BP. The results presented suggest that the new adenosine agonist CGS 21680A exerts a direct intrarenal effect on renal hemodynamics, but does not affect urine volume or sodium excretion or directly influence renin release.

This study compares the renal actions of the A2 selective adenosine agonist, CGS 21680A, with the A1 selective adenosine agonist, N6-cyclopentyladenosine (CPA), and the nonselective agonist, 5'-N-ethylcarboxamide adenosine (NECA), in the anesthetized dog. Initial receptor binding studies in dog brain demonstrated that CPA and CGS 21680A were selective for the A1 and A2 adenosine receptor, respectively, whereas NECA displayed slightly greater affinity for A1 than A2 adenosine receptors in the canine brain. Intravenous infusion of CGS 21680A (0.25 and 2.5 micrograms/kg/min) decreased blood pressure (BP) and increased heart rate (HR). CGS 21680A transiently increased renal blood flow (RBF) and either did not change or, at the highest dose infused, decreased glomerular filtration rate (GFR). Both urine volume (UV) and urinary sodium excretion (UNaV) also were decreased by CGS 21680A. At the lowest infusion rate (0.025 micrograms/kg/min) CGS 21680A produced a slowly developing increase in RBF, no change in GFR and a significant decrease in sodium excretion. Intravenous infusion of CPA (15 micrograms/kg/min) lowered BP and HR RBF and GFR. UNaV, UV and renin release also were inhibited by CPA. At a lower infusion rate (2.5 micrograms/kg/min), CPA markedly inhibited UNaV in the absence of a significant change in either BP or renal hemodynamic parameters. Infusion of NECA (0.01 and 0.1 micrograms/kg/min) lowered BP but did not change HR. Furthermore, RBF was increased by NECA, whereas UV and UNaV were inhibited in the absence of a change in GFR. These results may be explained by the relative selectivity of each analog for A1 or A2 adenosine receptors.

This study tested the hypothesis that angiotensin II acting through the angiotensin AT"1 receptor plays an important role in the control of gastric acid secretion. Basal gastric acid secretion and gastric blood flow were lower in Na^+-depleted animals, in which the renin-angiotensin system was activated, than in animals maintained on a normal Na^+ diet. Intravenous infusion of pentagastrin at 0.6 @mg/kg/min increased gastric acid secretion to a greater extent in normal Na^+ than in Na^+-depleted animals. In addition to stimulating gastric acid secretion, pentagastrin increased gastric blood flow by proportionally the same amount in both normal and low Na^+ animals. However, because basal gastric blood flow was considerably reduced in Na^+-depleted animals, the increase produced by pentagastrin extended only to the levels observed in non-pentagastrin-treated normal Na^+ animals. Lower gastric blood flow in response to pentagastrin may explain the smaller increase in gastric acid secretion observed in Na^+-depleted animals. In Na^+-depleted animals, the selective angiotensin AT"1 receptor antagonist losartan did not affect basal gastric acid secretion or gastric blood flow, suggesting the involvement of mechanisms other than angiotensin II. Following blockade of angiotensin AT"1 receptors, pentagastrin significantly increased gastric blood flow in Na^+-depleted animals to levels observed with infusion of the pentapeptide in normal Na^+ animals. The results suggest that the decrease in pentagastrin-stimulated acid secretion in Na^+-depleted animals is mediated by angiotensin II acting through the angiotensin AT"1 receptor, most probably through vascular mechanisms.

The purpose of this study was to determine if the changes in renal function acutely produced by an inhibitor of angiotensin converting enzyme (ACE) in the sodium-depleted conscious marmoset can be explained primarily by blockade of the renin-angiotensin system. Intravenous injection of a dose of the ACEI, enalaprilate (2 mg/kg), that produced a maximal lowering of blood pressure (BP), also decreased renal vascular resistance and increased renal blood flow. Glomerular filtration rate was unchanged by enalaprilat, leading to a fall in the filtration fraction. In comparison, a dose of the renin inhibitory monoclonal antibody, R-3-36-16 (0.1 mg/kg), that also produced a maximal fall in BP, produced similar changes in renal hemodynamics to those observed after administration of the ACEI. Combined administration of 2 mg/kg enalaprilat and 0.1 mg/kg R-3-36-16 produced changes in BP and renal hemodynamics similar to those produced by the same doses of either agent administered alone. Enalaprilat (2 mg/kg) significantly increased urine volume (UV) and urinary sodium excretion (UNaV). In contrast, these parameters were not significantly altered by 0.1 mg/kg R-3-36-16. However, when given at a 10-fold higher dose, the monoclonal antibody produced an increase in UNaV and UV identical to that produced by the ACEI alone. Enalaprilat did not increase UV and UNaV excretion to a greater extent than the high dose of the renin inhibitory antibody. These results demonstrate that acute administration of an ACEI affects BP and renal function in the sodium-depleted conscious primate primarily by inhibition of the renin-angiotensin system.

Mean arterial pressure (BP) was measured in conscious, spontaneously hypertensive rats (SHR). Oral administration of the angiotensin I-converting enzyme inhibitor (ACEI) CGS 16617 significantly lowered BP. In contrast, the thromboxane synthetase inhibitor (TxSI) CGS 12970 lacked an antihypertensive action in SHR. When administered concurrently, the TxSI significantly potentiated the antihypertensive actions of the ACEI. Inhibition of thromboxane synthetase did not potentiate the antihypertensive actions of metoprolol or verapamil, indicating that a specific interaction exists between a TxSI and an ACEI. The antihypertensive actions of CGS 16617 also were potentiated by the cyclooxygenase inhibitor indomethacin, a result suggesting that CGS 12970 may enhance the action of CGS 16617 by inhibiting the action of vasoconstrictor prostaglandins produced after administration of an ACEI. The potentiation of the antihypertensive actions of CGS 16617 by CGS 12970 remained unaffected by either the kallikrein inhibitor aprotinin or a bradykinin receptor antagonist. Thus, although the interaction between an ACEI and a TxSI is a prostaglandin-dependent mechanism, it is not mediated by endogenous kinins. Inhibition of thromboxane synthetase significantly stimulated renin release and significantly attenuated the pressor response to exogenously administered angiotensin II. An increase in the dependency of BP upon the renin-angiotensin system and attenuation of the vascular actions of angiotensin II may serve to explain the potentiation of the antihypertensive action of ACEI after inhibition of thromboxane synthetase. The interaction between ACEI and TxSI was not restricted to SHR, because a TxSI potentiated the actions of an ACEI in both normotensive and deoxycorticosterone acetate/Na hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)