Effects of pregnancy and lactation on lipolysis of ewe adipocytes induced by beta-adrenergic stimulation.

During pregnancy and lactation, three phases of beta-adrenergic stimulation of lipolysis appeared in adipocytes isolated from omental adipose tissue of ewes: During the first 90 days of pregnancy, there was a fall in the maximal lipolytic effect of isoproterenol. The maximum response to beta-lipolytic stimulus was reduced by 38% on day 90 (815 nmol/2 h/10(6) cells, compared to 1304 for controls) without any change in system sensitivity. Between days 90 and 120 of pregnancy (switch in adipose metabolism), this lipolytic effect increased progressively and became significantly larger (34%) than in non-pregnant ewes around parturition. The system sensitivity was then higher (0.05-0.11 vs. 0.21 microM) and remained so throughout lactation. During the first 3 weeks of lactation, this stimulated rate was twice as great as in controls.