The Effect of Osmotic Pressure and Angiotensin II on Arginine Vasopressin Release from Guinea Pig Hypothalamo-Neurohypophyseal Complex in Organ Culture*

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Abstract
We have developed an organ culture system of the male guinea pig hypothalamo-neurohypophyseal complex (HNC) and investigated the effect of various osmotic agents and angiotensin II on arginine vasopressin (AVP) release in vitro. On the fifth day in culture, ouabain-sensitive ATPase activity was 0.83 ± 0.11 mmol Pi/mg protein·h (mean ± sem), which was 67% of that on the first day in culture. On the fifth day, [6-3H]thymidine incorporated into DNA in the explants of HNC was 1205 ± 185 cpm/μg DNA. This was significantly inhibited by 1.8 · 10−6m puromycin (P < 0.001). Elevation of KCl concentration in the medium resulted in a 470 ± 38% increase in AVP concentration. The response of the explants to medium containing an elevated NaCl concentration was a 298 ± 31% increase in AVP release. This response was inhibited by the addition of tetrodotoxin to the culture medium. Angiotensin II caused the release of AVP into the culture medium from the explants in a dose-dependent manner. [Sar1, Ile8]Angiotensin II alone caused the release of AVP from the explants. The fact that a large dose of [Sar1, Ile8]angiotensin II plus angiotensin II results in AVP release equivalent to that of the angiotensin II analog alone is exactly what one would expect for specific receptors. Furthermore, AVP concentrations in culture medium made hypertonic with sodium chloride, sucrose, and mannitol were 298 ± 31% (P < 0.01), 251 ± 36% (P < 0.01), and 255 ± 59% (P < 0.05) of their control levels, respectively. The solutions of sodium chloride, sucrose, and mannitol at 310 mosmol/kg each caused AVP release from the explants of HNC in vitro, whereas equiosmotic solutions of glucose and urea proved to be poor osmotic stimuli for AVP release. (Endocrinology106: 1571, 1980)

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