Abstract
The role of central endogenous prostaglandin (PG) in the regulation of osmotically mediated vasopressin secretion under normal physiological conditions in rats was studied employing a prostaglandin synthetase inhibitor, indomethacin, and sensitive and specific radioimmunoassay for plasma arginine vasopressin.
A single dosage and doses for two and five days by s. c. injection of 5.0mg/kg BW of indomethacin, which can produce significant depletion of endogenous PG in the hypothalamus, resulted in a high correlation (r>0.9) between plasma arginine vasopressin (pAVP) and plasma osmolality (pOSM). This relation could be fitted to straight lines of the form pAVP=2.1 (pOSM-296)(N=10), pAVP=3.2 (pOSM-298)(N=13) and pAVP=0.9 (pOSM-295.6)(N=10), after i. p.injection with hypertonic saline, for the three dosages, respectively. The control regression lines could be described by relations of the form pAVP=2.9 (pOSM-298)(N=11), pAVP=3.1 (pOSM-299)(N=8) and pAVP=1.1 (pOSM-296.9)(N=13), respectively. The slope and intercepts (on the osmolality axis) were thus comparable with those of the control group, which had not been influenced by plasma urea nitrogen, glucose or blood volume.
These results suggest that the administration of indomethacin did not influence the osmoregulation of AVP directly.
From this evidence, we conclude that central endogenous PG has no primary role in the control of the osmoregulation of arginine vasopressin secretion under normal physiological conditions.
