Fat mobilisation in short days is not associated with altered noradrenergic sensitivity of adipocytes in Djungarian Hamsters

Abstract

One of the primary physiological responses of the Djungarian hamster to short photoperiods is a reduction in body weight with fat mobilisation. The depletion of fat to a minimum level may be regulated either in the periphery, through the sensitivity of adipocytes to hormonal stimulation, or centrally, via adjustments in efferent activity. To investigate this, we examined the lipolytic pathway in fat cells from animals at various stages of entrainment to long or short photoperiod. Short photoperiod exposure of up to a 10-week duration was without effect on basal glycerol release by unstimulated cells or on the ability of norepinephrine or an adenosine analogue to stimulate or inhibit lipolysis, respectively. Prolonged exposure to short photoperiod reduced basal glycerol release, but adipocytes retained their sensitivity to hormonal stimulation. Short photoperiod had no effect on the density or affinity of membrane-bound β-adrenergic or adenosine receptors, or upon the ability of isoproterenol or forskolin to stimulate adenylate cyclase in adipocyte membranes. This suggests that the regulation of fat depletion in short photoperiod is determined centrally and does not involve alterations in adipocyte sensitivity and, in particular, the desensitisation of the adipocyte β-adrenergic receptor-linked adenylate cyclase pathway.