Impaired secretion of epinephrine in response to insulin among hypophysectomized dogs

Arginine-vasopressin mediates central and peripheral glucose regulation in response to carotid body receptor stimulation with Na-cyanide

Hypoxic stimulation of the carotid body receptors (CBR) results in a rapid hyperglycemia with an increase in brain glucose retention. Previous work indicates that neurohypophysectomy inhibits this hyperglycemic response. Here, we show that systemic arginine vasopressin (AVP) induced a transient, but significant, increase in blood glucose levels and increased brain glucose retention, a response similar to that observed after CBR stimulation. Comparable results were obtained after intracerebral infusion of AVP. Systemic AVP-induced changes were maintained in hypophysectomized rats but were not observed after adrenalectomy. Glycemic changes after CBR stimulation were inhibited by pharmacological blockage of AVP V1a receptors with a V1a-selective receptor antagonist ([β-Mercapto-β,β-cyclopentamethylenepropionyl1,O-me-Tyr2, Arg8]-vasopressin). Importantly, local application of micro-doses of this antagonist to the liver was sufficient to abolish the hyperglycemic response after CBR stimulation. These results suggest that AVP is a mediator of the hyperglycemic reflex and cerebral glucose retention following CBR stimulation. We propose that hepatic activation of AVP V1a receptors is essential for this hyperglycemic response.

The role of the pituitary-adrenocortical axis in reflex responses of the adrenal medulla of the dog

1. The release of catecholamines from the adrenal medulla, in response to carotid body hypoxia, may outlast the stimulus by more than 30 min. 2. After denervation of the adrenal gland the immediate release of catecholamines in response to carotid hypoxia is abolished, but the prolonged release remains. 3. The prolonged release of catecholamines is abolished by cycloheximide. 4. Both corticotrophin in vivo and hydrocortisone in the isolated perfused adrenal gland release adrenomedullary catecholamines. 5. It is concluded that a component of the response of the adrenal medulla to carotid body hypoxia is mediated by corticotrophin and corticosteroid release.

The reflex release of adrenaline and noradrenaline from the adrenal glands of cats and dogs

1. We have studied the release of noradrenaline and adrenaline from the adrenal glands of dogs and cats in response to the lowering of carotid sinus pressure (baroreceptor tests) and to the perfusion of the vascularly isolated carotid bifurcations with hypoxic blood (chemoreceptor tests). 2. In cats, the resting output of catecholamines had a ratio of noradrenaline to adrenaline of 1:1. The ratio in the incremental release during baroreceptor tests rose to 3:1, and during chemoreceptor tests it fell to 1:6. 3. In dogs, the ratio of noradrenaline to adrenaline at rest was 1:4. The ratio did not change over a wide range of outputs during baroreceptor tests, chemoreceptor tests and splanchnic nerve stimulation. 4. The release of catecholamines in response to baroreceptor tests in the cat was abolished by hexamethomium bromide at doses that did not diminish the response to chemoreceptor tests.

Preferential secretion of adrenaline or noradrenaline by the cat adrenal in vivo in response to different stimuli

1. The concentrations of adrenaline and noradrenaline in the adrenal vein and the adrenal gland of the cat were studied in response to different stimuli leading to increased catecholamine (CA) secretion.2. Haemorrhage and hypoglycaemia, but not acute exposure to cold or intravenous administration of cocaine, induced considerable increases in total catecholamine secretion.3. The ratio of the concentration of adrenaline to noradrenaline in adrenal vein plasma during the control period was higher than the ratio in the adrenal gland itself.4. Haemorrhage increased noradrenaline secretion considerably more than adrenaline secretion so that the ratio of the concentration of adrenaline to noradrenaline in adrenal vein plasma was significantly lower than in the adrenal gland itself.5. Hypoglycaemia induced by insulin increased catecholamine secretion, with the adrenaline to noradrenaline ratio significantly higher than in the adrenal gland itself.6. Hypothermia resulted in a fall of the initial high ratio of adrenaline to noradrenaline, to a value similar to that in the adrenal gland.7. Neither cocaine nor changes in adrenal plasma flow affected the adrenaline to noradrenaline ratio in adrenal vein blood.8. It is concluded that preferential release from the adrenal gland of either adrenaline or noradrenaline is possible in vivo in response to different stimuli.