Substance P-like peptides and vasopressin release from posterior pituitary lobe incubated in situ after intracarotid injections of hypertonic solution in rats.

The experiments were performed on male rats, drinking 2% NaCl solution ad libitum for 12 days instead of tap water. The pituitary gland was exposed by the transpharyngeal approach under urethane-chloralose anaesthesia. The posterior lobe remained in neural and partial vascular connection with the hypothalamus, whereas the anterior lobe was entirely removed. Samples of the outflow medium from the incubated in situ rat posterior pituitary lobe were collected during 30 min intervals. Substance P-like peptides and vasopressin activities were assayed by the biological tests. Injections of hypertonic solution into the internal carotid artery did not change vasopressin release, but induced an increase in Substance P release from the posterior pituitary lobe into the incubation medium. Under conditions of unexcitability of the osmosensitive cells, triggering vasopressin release, the injection of hypertonic solution into the internal carotid artery stimulated the Substance P-like peptides release from the posterior pituitary lobe.