The Ca2+-mobilizing actions of vasopressin and angiotensin differ from those of the alpha-adrenergic agonist phenylephrine in the perfused rat liver.
A Ca2+-sensitive electrode was used to study net Ca2+-flux changes induced by the administration of phenylephrine, vasopressin and angiotensin to the perfused rat liver. The studies reveal that, although the Ca2+ responses induced by vasopressin and angiotensin are similar, they are quite different from the Ca2+ fluxes induced by phenylephrine. The administration of phenylephrine is accompanied by a stimulation of a net amount of Ca2+ efflux (140 nmol/g of liver). A re-uptake of a similar amount of Ca2+ occurs only after the hormone is removed. In contrast, the administration of vasopressin or angiotensin to livers perfused with 1.3 mM-Ca2+ induces the release of a relatively small amount of Ca2+ (approx. 40 nmol/g of liver) during the first 60 s. This is followed by a much larger amount of Ca2+ uptake (70-140 nmol/g of liver) after 1-2.5 min of hormone administration, and a slow efflux or loss of a similar amount of Ca2+ over a period of 6-8 min. At lower concentrations of perfusate Ca2+ (less than 600 microM) these hormones induce only a net efflux of the ion. These results suggest that at physiological concentrations of extracellular Ca2+ the mechanism by which alpha-adrenergic agonists mobilize cellular Ca2+ is different from that involving vasopressin and angiotensin. It seems that the hormones may have quite diverse effects on Ca2+ transport across the plasma membrane and perhaps organellar membranes in liver.
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D010477:Perfusion; D010656:Phenylephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D000804:Angiotensin II; D001127:Arginine Vasopressin; D010656:Phenylephrine; D005947:Glucose; D002118:Calcium