Effects of dopamine and morphine on immunoreactive somatostatin and LH-releasing hormone secretion from hypothalamic fragments in vitro.
Dopamine and morphine modulate GH and LH release, probably at a hypothalamic locus. To investigate this in more detail, we studied the influence of these substances on somatostatin and LH-releasing hormone (LHRH) release from rat hypothalamic fragments in vitro. Hypothalamic fragments were incubated in Earle's medium. After 60 min of preincubation, medium from two 20-min incubations was collected and somatostatin and LHRH levels measured by radioimmunoassay. Dopamine (10 nmol/1-0.1 mmol/l) induced a progressive increase (r = 0.41; P less than 0.01) in basal somatostatin levels. K+ (30 mmol/l)-induced somatostatin release was also increased (r = 0.54; P less than 0.01) by increasing doses of dopamine. Metoclopramide (10 mumol/l) blocked the dopamine (1 mumol/l)-induced increase in somatostatin release. No significant relationship between dopamine and LHRH was found either basally or after K+ (30 mmol/l) stimulation. Basal somatostatin was negatively correlated (r = -0.63; P less than 0.01) with morphine concentrations. No significant correlation was found after K+ (30 mmol/l) depolarization. Basal LHRH release was not influenced by morphine, while K+ (30 mmol/l)-induced release was significantly lower than controls only at a concentration of 10 nmol/l. These results suggest that dopamine and morphine act at a hypothalamic level to modulate GH release through alterations in somatostatin secretion. Dopamine and morphine have no consistent effect on hypothalamic LHRH release.
Lengyel
A M
AM
Grossman
A
A
Bouloux
P M
PM
Rees
L H
LH
Besser
G M
GM
D000818:Animals; D004298:Dopamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008787:Metoclopramide / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000378:metabolism*; D013268:Stimulation, Chemical
D007987:Gonadotropin-Releasing Hormone; D013004:Somatostatin; D009020:Morphine; D008787:Metoclopramide; D004298:Dopamine