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The effects of chronic dietary sodium chloride (NaCl) consumption on renal function and brain dopamine receptors were studied in adult, male normotensive rats. Compared to rats maintained on the normal NaCl (0.33%) diet, animals maintained on the low NaCl (0%) diet for 4 weeks exhibited significant increases in plasma aldosterone, chloride and changes in urinary electrolyte excretion. In contrast, rats maintained on the high NaCl (8%) diet for 4 weeks demonstrated significant increases in urine volume and urinary sodium, chloride and dopamine excretions and water intake. Rats fed the high NaCl diet displayed a 42-59% decrease (p < 0.001-0.05) in D1 binding in the nucleus accumbens (NA), olfactory tubercle (OT) and the striatum (STM), without any effects on D2 binding in these brain regions. Rats maintained on the low NaCl diet also demonstrated decreased D1 binding in the ventral (24%, p < 0.02) and lateral (29%, p < 0.01) STM, but not in the OT, NA, entopeduncular nucleus and substantia nigra. Rats fed low or high NaCl diets exhibited a 35-180% increase (p < 0.01-0.05) in D2 binding in several mid-brain areas (e.g. hypothalamus, thalamus and hippocampus) and hindbrain regions (e.g. superior colliculus and nucleus tractus solitarius) without affecting the D1 binding. These data indicate that chronic modification of dietary salt intake profoundly affects the renal handling of sodium/water excretion and leads to selective up- and/or down-regulation of DA receptor subtypes in different areas of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

In the present studies, the pharmacology and regulation of the functional muscarinic receptors on HSDM1C1 cells were probed using phosphoinositide (PI) turnover assays. In addition, the receptor binding of the putative M3-selective radioligand, [3H]4-DAMP, to cell homogenates was characterized. Carbachol (EC50 = 9 microM), (+)muscarine (EC50 = 4.5 microM) and cis-dioxolane (EC50 = 0.72 microM) were full agonists which stimulated PI turnover by 13.3 +/- 1.0 fold above basal values. The potencies of numerous agonists in this assay system were relatively similar to their affinities in receptor binding assays. Exposure of HSDM1C1 cells to 10 nM-10 microM muscarine during the last 24h of [3H]myo-inositol-labeling resulted in a concentration-dependent reduction in the cis-dioxolane affinity and maximal PI response induced by subsequent treatment with cis-dioxolane. Pertussis toxin (5-2000 ng/ml) caused a partial reduction in the cis-dioxolane-induced PI turnover. Likewise, exposure of the HSDM1C1 cells to an active phorbol ester (TPA) resulted in a partial inhibition of the cis-dioxolane-induced (100 microM) PI turnover. The half-maximal effect of TPA was produced at 1.8 +/- 0.3 nM. [3H]4-DAMP binding to cell homogenates was of high affinity (Kd = 0.19 +/- 0.04 nM) and moderate capacity (Bmax = 201 +/- 22 fmol/mg protein). The pharmacological specificity (4-DAMP > p-FHHSiD > dicyclomine > pirenzepine > methoctramine > AFDX-116 > gallamine) resembled that for [3H]NMS binding and correlated well with that observed for inhibition of PI turnover. These studies further support the identification of M3 receptors on HSDM1C1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin (BK) and its analogs (1 nM-100 microM) stimulated phosphoinositide (PI) turnover in murine fibrosarcoma (HSDM1C1) cells in a concentration-dependent manner. The relative potencies (EC50) were: BK = 48 +/- 4 nM; Lys-BK = 39 +/- 3 nM; Met-Lys-BK = 158 +/- 33 nM, Des-Arg9-BK = 2617 +/- 598 nM (means +/- SEM, n = 3-14). All these analogs were full agonists and they produced up to 5.4 +/- 0.4-fold stimulation of PI turnover at the highest concentration (10-100 microM) of the peptides. In contrast, the analogs [D-Arg0-HYP3-Thienyl5,8-D-Phe7]-BK (HYP3-antagonist), [D-Arg0-HYP3-Thienyl,5,8-D-Phe7]-BK (Thienyl antagonist) and Des-Arg9-Leu8-BK were inactive, as agonists, at 0.1 nM-1 microM in this system. These data suggested that BK-induced PI turnover in these cells was mediated via B2-type of BK receptors. This was confirmed further by the fact that both the B2-selective Hyp3- and Thienyl-antagonists inhibited BK-induced PI turnover with KBS of 369 +/- 51 nM and 368 +/- 118 nM respectively while the B1-selective antagonist, Des-Arg9-Leu8-BK, was inactive at 1 microM. [3H]BK receptor binding studies revealed two binding sites, one with high affinity (Kd = 0.24 +/- 0.06 nM; Bmax = 1.4 +/- 0.4 pmol/g tissue) and the other with low affinity (Kd = 18.5 +/- 0.95 nM; Bmax = 25.1 +/- 0.52 pmol/g tissue), on HSDM1C1 cell homogenates. The rank order of affinity of BK analogs at inhibiting specific [3H]BK binding was similar to that found for PI turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of centrally and peripherally administered dopamine D1 and D2 specific compounds on core body temperature in mice was investigated. Quinpirole (LY-17155), a D2 agonist, induced a dose-dependent fall in body temperature (2.4-11.6%; p less than 0.003) when injected intraperitoneally (ip, 0.3-3.0 mg/kg) and intracerebroventricularly (icv, 0.1 mg/kg). This quinpirole-induced (1.0 mg/kg, ip) hypothermia was reversed by the central and peripheral administration of the D2 antagonists S-(-)-sulpiride (3.0-30.0 mg/kg, ip; 0.1-3.0 mg/kg, icv) and spiperone (0.03 and 0.1 mg/kg, ip; 0.03-3.0 mg/kg, icv). Domperidone, a D2 antagonist which does not cross the blood brain barrier, had no effect on quinpirole-induced hypothermia (1.0-10.0 mg/kg, ip). Domperidone partially reversed quinpirole-induced hypothermia at 0.1-30.0 mg/kg, icv. The D1 agonist, SKF-38393 at a high dose of 10.0 mg/kg, ip mildly attenuated quinpirole-induced hypothermia (a 1.8% increase in temperature). SKF-38393 at 10.0 mg/kg, icv potentiated quinpirole-induced hypothermia. SCH-23390 (0.1-3.0 mg/kg, ip), a D1 antagonist, had no effect on quinpirole-induced hypothermia and potentiated the hypothermia when administered icv. An ineffective icv dose of spiperone (0.01 mg/kg) in reversing quinpirole-induced hypothermia was rendered effective by prior administration of SCH-23390 (0.1-3.0 mg/kg, icv) but not by SKF-38393 (1.0-10.0 mg/kg, icv). These data suggest a central D2 receptor mechanism mediating hypothermia in mice which is capable of being modulated by the D1 receptor.

The biochemical and pharmacological properties of [3H]MK-801 binding to the N-methyl-D-aspartate (NMDA) receptor-channel in homogenates of mouse, guinea pig and dog brain, dog cerebral cortex and rat spinal cord were determined using radioligand binding techniques. Specific [3H]MK-801 binding increased linearly with increasing tissue concentration and in general represented 80-93% of the total binding at 6-8 nM radioligand concentration. [3H]MK-801 interacted with brain and spinal homogenates with high affinity. The dissociation constants (KD) for all tissues studied were similar ranging between 7.9 and 11.9 nM, whereas the maximum number of binding sites (Bmax) showed a wide, tissue-dependent range (0.1-6.75 pmol/mg protein). The rank order of tissue enrichment was found to be as follows: mouse brain much greater than dog cerebral cortex much greater than dog brain much greater than guinea pig brain much greater than rat spinal cord. Specific [3H]MK-801 binding in rodent and dog brain, dog cerebral cortex and rat spinal cord exhibited a similar pharmacological profile (correlation coefficients = 0.93-0.99). The rank order of potency of unlabelled compounds competing for [3H]MK-801 binding was: (+)MK-801 greater than (-)MK-801 greater than phencyclidine greater than (-)cyclazocine much greater than (+)cyclazocine greater than or equal to ketamine greater than (+)N-allyl-N-normetazocine greater than (-)N-allyl-N-normetazocine greater than (-)pentazocine greater than (+)pentazocine. NMDA, Kainate, quisqualate and several other compounds failed to inhibit [3H]MK-801 binding at 100 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

[3H](3-Me-His2) thyrotropin-releasing hormone ([3H]MeTRH) bound to TRH receptors in rodent, rabbit and dog brain and spinal cord (SC), and in rat, sheep, bovine and dog anterior pituitary (PIT) glands, with high affinity (dissociation constants, KdS = 5-9 nM; n = 3-4) but to different densities of these sites (Bmax range 6-145 fmol/mg protein) (rabbit SC greater than sheep PIT much greater than G.pig brain greater than dog brain greater than rat brain greater than bovine and dog PIT). Various TRH analogs competitively inhibited [3H]MeTRH binding in these tissues with a similar rank order of potency: MeTRH greater than TRH greater than CG3703 greater than or equal to RX77368 greater than or equal to MK-771 greater than TRH Glycinamide greater than Glu1-TRH much greater than CG3509 greater than or equal to NVal2-TRH much much greater than TRH free acid much much greater than and cyclo-His-Pro, indicating a pharmacological similarity of CNS and pituitary TRH receptors. While most TRH analogs displaced [3H]MeTRH binding with a similar potency in the different species, TRH exhibited a 2-fold lower affinity in the rat and G.pig brain than in other tissues of other species. Similarly, CG3703 was 2.4-4.5 times more active in the rabbit brain than in the rodent and dog brain, and also more potent in the rabbit brain as compared to the sheep PIT.(ABSTRACT TRUNCATED AT 250 WORDS)