THE EFFECT OF GRADUAL CHANGES IN TEMPERATURE ON THE RELEASE OF HORMONES FROM NERVE ENDINGS ISOLATED FROM BOVINE NEURAL LOBES¹

Abstract

Abstract— Homogenates of bovine neural lobe tissue were fractionated by differential centrifugation at 20°C or at 4°C and the distribution of activities of vasopressin and oxytocin among the fractions was compared. The ratio of total hormone to protein (mg) in the homogenate was similar at the two temperatures. At 20°C a much smaller proportion of the total hormone was recovered in the soluble fraction (100,000 gav supernatant), than at 4°C with a corresponding increase in recovery in the nerve‐ending fraction (800–3000 g sediment). Nerve endings isolated at 4°C did not, when incubated, release hormone in response to changes in temperature. Nerve endings isolated at 20°C released hormone when the temperature was reduced below 15°C. Gradual reduction in temperature led to hormone release unaccompanied by lactate dehydrogenase release. Incubation of nerve endings for 10 min at 10°C increased the release of vasopressin and of neurophysin without any increase in lactate dehydrogenase. These results demonstrate that release of vasopressin by cold stimulation occurs by way of exocytosis.

Gadolinium ions inhibit exocytotic vasopressin release from the rat neurohypophysis.

“…Using synaptosomal preparations it was further shown that the cold-induced, calcium-independent vasopressin release is exocytotic (Baker & Hope, 1976). Therefore, the cold-induced vasopressin release seems to be a useful tool to find out whether Gd3+ affects exocytosis distal to the calcium entry.…”

Hormone release from isolated nerve endings of the rat neurohypophysis.

“…It is of interest to know that neurosecretosomes were first isolated more than twenty years ago (La Bella & Sanwal, 1965) but that studies by many groups on such nerve terminals have been very disappointing (Baker, Vilhardt & Hope, 1975;Baker & Hope, 1976;J. J. Nordmann, unpublished).…”

“…Although the neurosecretosomes have been shown to have a membrane potential which diminishes with increasing external K+ concentration (Nordmann, Desmazes & Georgescault, 1982) previous studies failed to detect an enhanced release of hormones under such conditions. To our knowledge cold was the only stimulus which could induce the release of AVP from nerve terminals (Baker et al 1975;Baker & Hope, 1976). Although we do not know exactly the differences between the present preparation and those used previously by us or by others, we can attempt to speculate on the nature of these differences.…”

Inhibition by Dopamine of Oxytocin Release from Isolated Posterior Lobe of the Hypophysis of the Rat; Disinhibitory Effect of <i>β</i>-Endorphin/Enkephalin

“…The finding of Baker and Hope [3] that oxytocin is released into an incubation medium when pituitary tissue is incubated in vitro at tem peratures between 0 and 15 C supports this suggestion since under these conditions a release of endorphins has been reported [23,35], At low temperatures, however, a partial inhibition of membrane ATPase is also expected [38]. Since it has been shown [36] that Na K 1 -activated ATPase activity of the neural lobe of the bovine pituitary gland is bound to a membrane fraction, it is also possible that the release in response to cold could be associated with an inhibition of the enzyme activity.…”