title: Modulation by fenoldopam (SKF 82526) and bromocriptine of the electrically evoked release of vasopressin from the rat neurohypophysis. Effects of dopamine depletion.
abstract: Single neurointermediate lobes were fixed by their stalks to a platinum wire electrode and incubated in Krebs-bicarbonate solution. Vasopressin release into the medium was determined by a radioimmunoassay. Vasopressin secretion was increased by electrical stimulation (15 Hz, 10 s trains with 10 s intervals for 10 min). Fenoldopam (SKF 82526) had a dual effect on vasopressin release, 30 nM decreasing (by 30%) and 3 microM increasing (by 32%) the evoked vasopressin secretion. The facilitatory effect of fenoldopam was antagonized in a concentration-dependent manner by flupenthixol but not by sulpiride. Sulpiride (1 microM) prevented the inhibitory effect of fenoldopam (30 microM). After pretreatment of the rats with the dopamine depleting agent, Ro4-1284 (2 mg/kg i.p. 1 h before the experiments), the evoked vasopressin release was decreased by 21% and the inhibitory effect of fenoldopam disappeared, but the facilitatory effect of fenoldopam was already seen at 30 nM. Similarly, bromocriptine (1-10 microM) decreased the evoked vasopressin release from untreated neurointermediate lobes by 30-40% but increased the vasopressin release by 30% after pretreatment with Ro4-1284. The present findings further support the concept that vasopressin from the neurohypophysis is modulated by dopaminergic mechanisms. Facilitatory effects are mediated via D 1 and inhibition via D 2 receptors. The presence of endogenous dopamine seems to be necessary for the inhibitory effects to occur.
mesh_terms: D000818:Animals; D001552:Benzazepines / Q000494:pharmacology*; D001971:Bromocriptine / Q000494:pharmacology; D004298:Dopamine / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D018818:Fenoldopam; D066298:In Vitro Techniques; D010904:Pituitary Gland, Posterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D014667:Vasopressins / Q000378:metabolism*
chemical_list: D001552:Benzazepines; D011954:Receptors, Dopamine; D014667:Vasopressins; D001971:Bromocriptine; D018818:Fenoldopam; D004298:Dopamine