Neurohypophyseal vasopressin in the Syrian hamster: response to short photoperiod, pinealectomy, melatonin treatment, or osmotic stimulation.
In the present study, the effect of photoperiod on vasopressin content in the pituitary neurointermediate lobe (NIL), as well as the ability of pinealectomy to prevent and melatonin to mimic the short photoperiod-induced changes in NIL vasopressin were studied in male Syrian hamsters. The ability of melatonin to modify the hyperosmotically stimulated vasopressin release was also determined. Exposure to short photoperiod (SD) for 4 or 10 weeks increased vasopressin content in the hamster NIL. In long photoperiod (LD)-exposed hamsters, pinealectomy induced a decrease in NIL vasopressin content, whereas no effect of melatonin injections on vasopressin storage in the NIL was detected. In SD-exposed animals, pineal removal failed to alter vasopressin content in the NIL. Hypertonic saline administration led to the expected decrease in vasopressin content in the NIL both in vehicle- and melatonin-treated animals. The hyperosmotically stimulated release of vasopressin was not modified by previous treatment with melatonin. The data from the present study show that, in male Syrian hamsters, exposure of animals to SD increases the vasopressin content in the posterior pituitary, but these changes appear not to be mediated by SD-induced changes in melatonin secretion. Furthermore, the exposure of animals to SD prevents the pinealectomy-induced changes in NIL vasopressin content. Melatonin does not modify the hyperosmotically stimulated vasopressin release in the male Syrian hamster.
Juszczak
M
M
Department of Pathophysiology, Medical University of Lodz, Poland.
Debeljuk
L
L
Stempniak
B
B
Steger
R W
RW
Fadden
C
C
Bartke
A
A
D000818:Animals; D006224:Cricetinae; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D009997:Osmotic Pressure; D017440:Photoperiod; D010870:Pineal Gland / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D014667:Vasopressins / Q000378:metabolism*
D014667:Vasopressins; D008550:Melatonin