Separation of periventricular dopaminergic and alpha-adrenergic systems from the vasopressin-secreting mechanisms activated by prostaglandin D2.

The aim of this study was to evaluate periventricular dopaminergic and alpha-adrenergic receptor functions in vasopressin (AVP) secretion elicited by central applications of prostaglandin D2 (PGD2) in conscious rats. Intracerebroventricular (i.c.v.) injections of PGD2 (70.9 nmol (25.0 micrograms] produced transient rises in plasma AVP 5 min later, without increasing plasma osmolality, sodium and hematocrit. Arterial pressure and heart rate before and after the PGD2 administrations were not significantly different from those of control rats receiving its vehicle. The PGD2-induced AVP response was not significantly altered by the prior i.c.v. administrations (0.15 mumol) of dopamine receptor antagonists, SCH 23390 or sulpiride, and an alpha-adrenoreceptor antagonist, phenoxybenzamine, performed 10 min before the injections of PGD2. The pretreatments with these catecholamine antagonists were confirmed to significantly prevent the augmentations in plasma AVP 5 min after the i.c.v. applications of 0.75 mumol dopamine or phenylephrine that were considerably larger than the PGD 2-induced AVP response. From these results, we concluded that dopaminergic and alpha-adrenergic receptors in the periventricular regions may not be involved in the AVP secretion stimulated by PGD2.