title: Demonstration of proximal tubular alpha-adrenoceptors in vivo.
abstract: Receptors for parathyroid hormone (PTH) in the renal tubule are coupled to adenylate cyclase stimulation. PTH causes a rise in urinary cAMP by leakage from adenylate cyclase stimulation. PTH causes a rise in urinary cAMP by leakage from cells of the proximal convoluted tubule. The effects of alpha-adrenergic agonists and antagonists on the urinary cAMP response to PTH were investigated in anaesthetized rats in vivo. Injection of PTH (15 u/kg i.v.) produced an increase in urinary cAMP from 1.7 (s.e.m. = 0.3, n = 6) to 7.47 (s.e.m. = 0.7, n = 6) nmol cAMP/mumol creatinine in 30 min urine samples. Infusion of the alpha 2-adrenoceptor agonist clonidine at 1 microgram/kg per min caused a decrease in the cAMP response to PTH to 3.6 (s.e.m. = 0.5, n = 12) nmol cAMP/mumol creatinine. Infusion of the alpha 2-selective catecholamine alpha-methylnoradrenaline (1 microgram/kg per min) caused a similar reduction in urinary cAMP response to that observed with clonidine. The alpha-adrenoceptor antagonist phentolamine (100 micrograms/kg per min) enhanced the cAMP response to PTH and reversed the decreased response caused by clonidine. These results demonstrate the presence of alpha-receptors in the rat proximal convoluted tubule which oppose the actions of PTH in vivo.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000652:urine; D007687:Kidney Tubules, Proximal / Q000032:analysis* / Q000187:drug effects; D008297:Male; D010281:Parathyroid Hormone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000032:analysis* / Q000187:drug effects
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D010281:Parathyroid Hormone; D011942:Receptors, Adrenergic, alpha; D000242:Cyclic AMP