Enhanced lipolysis is not evident in adipocytes from exercise-trained SHR

Adipocytes from spontaneously hypertensive rats (SHR) are not as responsive to isoproterenol or dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP) stimulation compared with Sprague-Dawley or Wistar-Kyoto rats. Lipolytic activity in adipocytes from trained normotensive rats was enhanced in response to 1 microM isoproterenol and 0.5 mM dibutyryl cAMP but not in adipocytes from trained SHR. Decreases in isoproterenol-stimulated (1 microM) cAMP accumulation were evident in adipocytes from trained normotensive rats but not in adipocytes from trained SHR. Basal and agonist-induced lipolysis in fat cells isolated from both normotensive rats and SHR immediately following a 60-min run was increased in both sedentary and trained rats. Adenylate cyclase activity in fat cell membranes was blunted in sedentary and trained SHR both in the absence and presence of 100 microM 5'-guanylyl imidophosphate. No apparent differences existed in antagonist affinity of binding sites for the antagonist dihydroalprenolol in normal rats or SHR. Evidence for a change in affinity of agonist isoproterenol might be indicated based on the enhanced potency of isoproterenol to stimulate lipolysis in trained normal rats. beta-Adrenergic receptor density and antagonist affinity were not different in normotensive rats and SHR in response to training. However, displacement of [3H]dihydroalprenolol in adipocytes from SHR required greater concentrations of isoproterenol compared with adipocytes from normotensive rats, further suggestive of increased agonist affinity of binding sites in normal rats. These data suggest a postreceptor lesion of the lipolytic pathway in adipocytes from spontaneously hypertensive rats, possibly at the guanine nucleotide regulatory protein level.(ABSTRACT TRUNCATED AT 250 WORDS)