Are the short‐photoperiod‐induced decreases in serum prolactin responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters?

Abstract

Serum prolactin (PRL) decreases in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters following short-photoperiod exposure. Both species also exhibit short-photoperiod-induced changes in body and lipid mass, but in opposite directions; Syrian hamsters increase and Siberian hamsters decrease their body weight, changes reflected nearly exclusively in their carcass lipid content. The purpose of these experiments was to determine whether the photoperiod-induced changes in PRL were responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters by using the strategy of experimentally producing serum PRL levels opposite to those normally associated with the photoperiod in which the animals were housed. In long photoperiods serum PRL was reduced to short-day levels by subcutaneous (s.c.) CB-154 (bromoergocryptine, a dopamine agonist) injections. In short photoperiods, serum PRL was elevated to long-day levels in Syrian hamsters by ectopic pituitary explants, and in Siberian hamsters, serum PRL was elevated by chronic s.c. infusions of ovine PRL (oPRL). In both species, manipulations of serum PRL did not affect food intake, carcass composition, or the wet weight of various white and brown adipose tissue pads (WAT and BAT, respectively). Body weight increased in CB-154-treated Syrian hamsters and decreased in Siberian hamsters, an effect partially reversed by coadministration of oPRL in Syrian, but not Siberian, hamsters. Thus, lowering serum PRL to short-day levels in long-day-housed hamsters of both species mimicked the directional change in body weight appropriate for each species when they are exposed to short days. This effect of CB-154 on body weight may be a result of some as yet unidentified effect of dopaminergic stimulation on overall growth since 1) these changes in body weight were not reflected as changes in lipid mass, as occurs naturally following short-day exposure for each species, and 2) neither species exhibited a reciprocal change in body weight when serum PRL was experimentally elevated in short days. Alternatively, it may be that once the energetic responses to short-day exposure have been fully expressed, the ability of PRL to stimulate the target sites of action for PRL for these responses may be decreased. BAT protein content, cytochrome oxidase activity (measures of metabolic growth of this tissue), and retroperitoneal total and specific lipoprotein lipase (LPL) activities were increased by CB-154 treatment in Syrian hamsters.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracerebroventricular Administration of Bromocriptine Ameliorates the Insulin-Resistant/Glucose-Intolerant State in Hamsters

“…Available evidence suggests that the effects of bromocriptine to improve early morning glucose tolerance may be associated with increased insulin-mediated glucose disposal [19], whereas its effects on late afternoon glucose metabolism (when plasma free fatty acid levels are high in male hamsters [21]) may be focussed on insulin-mediated suppression of hepatic glucose production (table 1). The results of the present study demonstrate that, as in previous studies [7, 10, 23, 24, 25]bromocriptine significantly reduces weight gain without affecting food consumption. This indicates a possible increase or shift in energy expenditure, which has been associated with an increase in protein turnover and a decrease in lipogenesis [10].…”

Physiological mechanisms for food-hoarding motivation in animals

“…In hoarding studies with Syrian hamsters (Schneider & Buckley 2001), it appears that the hamsters naturally separate out into two groups of high and low hoarders. The body mass of each group, however, is the same, and for this species, body mass and body fat correlate well Bartness et al , 1987. Thus, for Syrian hamsters, the inverse relation between body mass/fat and food-hoard size is not supported (Schneider & Buckley 2001).…”

Brain-adipose tissue neural crosstalk

“…Even more remarkable is that this obesity is completely reversed when they are exposed to 'winter-like' SDs (e.g., 8 h light, 16 h darkness) and this rapid loss of body fat occurs voluntarily and without, at least initially, a decrease in food intake (e.g. , 21,93 ). In addition, unlike the other photoperiod-induced obesity models (e.g.…”