The Effect of Prostaglandins on the Release of Arginine Vasopressin from the Guinea Pig Hypothalamo-Neurohypophyseal Complex in Organ Culture*

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Abstract
The effect of prostaglandins (PGs) on arginine vasopressin (AVP) release was investigated using the male guinea pig hypothalamo-neurohypophyseal complex (HNC) in organ culture. The explants of HNC were used on the second day in culture. The culture medium containing PGE2 caused an increase in AVP release from the explants during a 10-min incubation period. AVP release was significantly increased at a PGE2 concentration of 2 × 10-8 M or more. AVP release was increased in a dose-dependent manner. PGF2α at concentrations of 1.4 × 10-7 and 1.4× 10-6 M also increased AVP release significantly. The explants in the group treated with 7.4 × 10-5 M indomethacin for 60 min before the experiment and throughout the experiment responded to 6.5 × 10-8 M angiotensin II with a 166 ± 42% increase in AVP release over control release. The response of explants to the addition of angiotensin II in this group was significantly lower (P < 0.05) than that in the group not treated with indomethacin, which was 439 ± 128% of the basal value (P < 0.05). The release of AVP in the group treated with indomethacin was 120 ± 15% of the basal value in response to a hypertonic solution of sodium chloride at 310 mosmol/kg HjO and was significantly lower (P < 0.05) than that in the group not treated with indomethacin (203 ± 30% of the basal value; P < 0.005). However, indomethacin did not alter basic release of AVP. These results suggest that PGE2 and PGF2α, increase AVP release from the explants of HNC in organ culture, although PGF2α has a relatively weaker effect than PGE2, and PGs may modulate the regulation of AVP release in response to angiotensin II and osmotic stimulation.