Short photoperiod effects on kidney growth in male Syrian hamsters

The transfer of Syrian golden hamsters from a long to a short photoperiod (SP) leads to reduced circulating levels of several anterior pituitary hormones including thyrotropin stimulating hormone (TSH), luetinizing hormone (LH) and follicle stimulating hormone (FSH), while growth hormone (GH) is unaffected. These hormonal changes are associated with accelerated rates of body weight gain and gonadal atrophy in this species, but the effects on growth of other organs, specifically the kidney, are unknown. In this study, the effect of SP treatment on kidney and body weights of intact and uninephrectomized male Syrian golden hamsters was evaluated. Seventy-two young adult male hamsters were acclimatized to long photoperiod (LP) consisting of a light/dark schedule of 14/10 hours (LD 14:10). Two weeks later one half of the animals were transferred to SP (LD 10:14) Subgroups of six hamsters underwent either left nephrectomy or sham left nephrectomy two, five and eight weeks after transfer to SP and were sacrificed two weeks after surgery. The relative kidney weights (kidney weights/100 g body weight) of the sham operated animals were significantly reduced after seven and ten weeks of SP treatment (p less than 0.01). Absolute kidney weights were depressed after eight (p less than 0.05) and ten weeks in SP. The percentage increase in the weight of the hypertrophied kidney following uninephrectomy was unaffected by SP. Differences in body weights were due to increased fat in SP-treated hamsters; nonetheless, the logs of kidney and body weights were highly correlated in both LP (r = 0.73) and SP (r = 0.78). Lean body weights, determined by body compositional analysis, were less well correlated with kidney weights in LP (r = 0.53) and unrelated in SP (r = 0.16). The mechanism retarding kidney growth was not elucidated, but may include SP-induced changes in TSH, LH, or a specific LH-like pituitary renotropin proposed by Nomura et al. (1982). The observation that compensatory renal growth proceeds despite inhibition of kidney growth in intact animals suggests that separate mechanisms regulate these processes.