ALPHA1-ADRENERGIC AND ARGININE-VASOPRESSIN STIMULATION OF INOSITIDE HYDROLYSIS IN RAT HEPATOCYTES IS UNALTERED IN SENESCENCE

Alpha1-adrenergic receptors in the liver support glucose counterregulation by stimulating glycogenolysis and gluconeogenesis. We have recently reported that senescence is accompanied by reductions both in the density of alpha1 receptors in liver homogenates and in the affinity of these receptors for agonists (Borst and Scarpace, 1990a). The present studies were undertaken to determine what consequences these reductions may have for agonist-stimulated second messenger production. To this end we measured the density of alpha1-adrenergic receptors and agonist-stimulated phosphoinositide (PI) hydrolysis in short-term hepatocyte cultures derived from young and senescent rats. Receptor density in hepatocytes was unchanged with age. PI hydrolysis response to epinephrine was alpha1 in nature, as it was fully blocked by prazosin. The epinephrine response was unchanged with age, both in maximum response and in sensitivity. Similarly, the response to arginine vasopressin (AVP) was also unchanged with age.