Effect of intravenous and intracarotid injections of hypertonic fluids on the release of melanocyte-stimulating hormone from the rat posterior pituitary lobe incubated in situ.

The posterior pituitary lobe of male rats under urethane anaesthesia was incubated in situ. The pituitary gland was exposed by thr transpharyngeal apprach. The posterior lobe remained in neural and partial vascular connexion with the hypothalamus, whereas the anterior lobe was entirely remobed. Incubation fluid was collected and its melanophore-stimulating activity was assayed in hypophysectomized frogs. No effect was observed after the i.v. injection of 1 ml 120 muM-NaC1 with 60 muM-CaC12 or isotonic NcC1 solution. Hypertonic solutions of 5% NaC1 and 25% glucose injected intravenously to the limit of 0-5% of the body weight, transiently enhanced the release of MSH from the posterior pituitary lobe by 66% (significant) and 15% (not significant) respectively. Intracarotid injection of 0-3 ml 5% NaC1 solution resulted in the highest increase (95%) of MSH release.