Sexual dimorphism in adrenergic regulation of hepatic glycogenolysis

Abstract

The total phosphorylase a plus b of hepatocytes isolated from females and incubated in the absence or presence of estradiol and progesterone at concentrations found in vivo does not vary during the estrous cycle. However, there is a slight but significant influence of the estrous cycle on basal and epinephrine-stimulated phosphorylase a activity, with a nadir being seen on diestrus. The relative contributions of the alpha- and beta-mediated pathways to phosphorylase a activation do not vary with the estrous cycle but are constant at 75 and 56%, respectively, of the response to 5 X 10(-8) M epinephrine. When the epinephrine-stimulated glucose release from glycogen stores in cells from females and males is compared, the release from the female is greater than that from the male, while the alpha-receptor-mediated stimulation in the female is comparable with that in the male. The beta-mediated pathway causes glucose release which averages 45% of that stimulated by epinephrine alone in cells from females. Basal cytosolic free calcium is similar in cells from males and females (142 vs. 149 nM, respectively). The epinephrine-stimulated increase in cytostolic free calcium (Cai) is greater in the male than the female at 10(-6) M (489 vs. 380 nM) but greater in the female than the male at 5 X 10(-9) M (54 vs. 27 nM). The changes in Cai are equivalent at intermediate epinephrine concentrations. When considered with our prior analysis of 45Ca efflux after adrenergic stimulation, this suggests there may be a sexual dimorphism in hepatocyte calcium transport systems. The glucose release for a given increase in Cai is greater in the female than the male probably due to the concomitant action of the beta-mediated increase in cAMP and the alpha-mediated increase in Cai. This supports the conclusion that the beta-mediated component does make a significant contribution to the catecholamine regulation of glycogenolysis in hepatocytes from adult female rats.