Osmotic pressure and angiotensin II stimulation of arginine vasopressin release from a guinea pig hypothalamo-neurohypophyseal complex in organ culture (author's transl)

Abstract

An organ culture system of a male guinea pig hypothalamo-neurohypophyseal complex (HNC) was established. On day 5 in culture, (Na+ -K+) ATPase activity was 0.83 +/- 0.11 mM Pi/mg prot/hr (mean +/- SEM): that is 67% of that on day 1 in culture. 3H-thymidine incorporated into DNA in the explants of HNC was 1,205 +/- 185 cpm/microgram DNA. The explants responded to the elevated KCl medium and the hypertonic solution of sodium chloride with a 470 +/- 38% and 298 +/- 31% increase in arginine vasopression (AVP) release, respectively. This response was inhibited by the addition of tetrodotoxin to the culture medium. AVP release from the explants in res-onse to angiotensin II increased significantly in a dose dependent manner. [Sar1, Ile8] angiotensin II, however, attenuated the response of the explants to angiotensin II when administered simultaneously with angiotensin II. These results suggest that angiotensin II and its analogue cause the AVP release from the explants in a competitive manner. The concentrations of AVP in the culture media made hypertonic with sodium chloride, sucrose and mannitol were 298 +/- 31% (p less than 0.01), 251 +/- 36% (p less than 0.01) and 255 +/- 59% (p less than 0.05) of their control values, respectively. The hypertonic solutions of sodium chloride, sucrose and mannitol caused AVP release from the explants in vitro, while the hypertonic solutions of glucose and urea were revealed to be poor osmotic stimuli on AVP release. These results support the concept of osmoreceptors to release AVP from the hypothalamo-neurohypophyseal axis.