Reduced oxygen consumption of brown adipocytes isolated from progesterone-treated rats.

It has been previously shown that responsiveness to noradrenaline is reduced in brown adipocytes isolated from estradiol-treated rats. The possibility that high plasma levels of progesterone could also alter adrenergic response was checked. The oxygen consumption of brown adipocytes isolated from control and progesterone-treated rats was monitored in basal conditions and in the presence of increasing concentrations of noradrenaline. In both situations, cells isolated from treated animals showed a lower respiratory rate than those from control animals. These results suggest that not only estradiol but also progesterone could modulate the adrenergic response of brown adipocytes. The study of alpha 1- and beta-adrenergic responses indicates that the beta-response parallels the general reduction in oxygen consumption, although the alpha 1-response seems to be more deeply depressed. Estimation of cell number in brown fat depots indicates some hyperplasia induced by progesterone; this increase in cell number could counterbalance partially but not totally the decreased cellular oxygen consumption at the organ level.