Role of alpha 1- and alpha 2-adrenoceptors in catecholamine-induced hyperglycaemia, lipolysis and insulin secretion in conscious fasted rabbits.
1. In conscious fasted rabbits an intravenous infusion of clonidine (2 micrograms kg-1 min-1) induced hyperglycaemia. The increase in blood glucose was accompanied by an inhibition of insulin secretion and basal lipolysis. 2. Yohimbine infused at a rate of 20 micrograms kg-1 min-1 suppressed clonidine-induced hyperglycaemia and blocked the inhibitory effect on insulin secretion mediated by the alpha 2-adrenoceptor agonist. 3. The intravenous infusion of amidephrine (10 micrograms kg-1 min-1) induced an increase in insulin secretion in the absence of patent hyperglycaemia. Prazosin, 0.3 mg kg-1 s.c. selectively antagonized the effect of amidephrine on insulin secretion. 4. Isoprenaline infusion (4.4 micrograms kg-1 min-1) evoked a significant increase in blood glycerol and immunoreactive insulin plasma levels. Both responses were clearly attenuated when alpha 2-adrenoceptors were simultaneously stimulated by selective (clonidine) and less selective (phenylephrine, 20 micrograms kg-1 min-1) agonists. 5. Amidephrine infusion did not induce appreciable changes in blood glycerol nor did it modify, isoprenaline-induced lipolytic response. 6. Simultaneous infusion of isoprenaline and amidephrine induced a remarkable increase in insulin secretion. 7. It is concluded that in normal fasted rabbits stimulation of alpha 2-adrenoceptors depresses basal and beta-adrenoceptor mediated lipolysis and insulin secretion. On the other hand, selective stimulation of alpha 1-adrenoceptors does not affect lipolysis but induces insulin release. Simultaneous stimulation of alpha 1- and beta-adrenoceptors potentiates the insulin secretory response.
Moratinos
J
J
Department of Pharmacology, School of Medicine, Universidad de Salamanca, Spain.
Carpene
C
C
de Pablos
I
I
Reverte
M
M
D000818:Animals; D002395:Catecholamines / Q000494:pharmacology*; D003000:Clonidine / Q000494:pharmacology; D006943:Hyperglycemia / Q000139:chemically induced*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008066:Lipolysis / Q000187:drug effects; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D002395:Catecholamines; D007328:Insulin; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D011433:Propranolol; D003000:Clonidine; D011224:Prazosin