title: Effect of short photoperiod on hypothalamic methionine-enkephalin and LHRH content and serum beta-endorphin-like immunoreactivity (beta-end LI) levels in golden hamsters.
abstract: Adult female golden hamsters were used to study the effect of short photoperiod on the endogenous opioid system and the effect of pinealectomy on the serum beta-endorphin-like immunoreactivity (beta-end LI) levels. Hamsters were housed under either long photoperiod (14L:10D) or short photoperiod (2L:22D) and the regularity of the estrous cycles was determined by daily vaginal exfoliative cytology. Hamsters under short photoperiod became acyclic after about 7 wk. At the end of 8 wk, all the hamsters were decapitated and medial basal hypothalamic (MBH) content of LHRH and methionine-enkephalin (met-enkephalin) were measured by specific radioimmunoassays (RIA). Both LHRH and met-enkephalin levels of the MBH were significantly elevated in the short-photoperiod hamsters as compared to the normally cycling control animals under long photoperiod. In a second experiment, the effect of pinealectomy (PNX) on the serum levels of beta-end LI in the short-photoperiod hamsters was determined. The serum beta-end LI levels were increased approximately threefold in the noncyclic hamsters housed under 8 wk of short-photoperiod conditions. Pinealectomized hamsters kept under 8 wk of short-photoperiod exhibited lower serum beta-end LI levels similar to those of normally cycling hamsters kept under long photoperiod. These results indicate a possible functional relationship between increased pineal activity (as a result of short photoperiod) and increased MBH met-enkephalin, LHRH, and serum beta-end LI levels.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae; D003624:Darkness; D004723:Endorphins / Q000097:blood*; D004744:Enkephalin, Methionine / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism*; D007033:Hypothalamus, Middle / Q000502:physiology; D007700:Kinetics; D008027:Light; D008647:Mesocricetus; D010870:Pineal Gland / Q000502:physiology*; D011957:Receptors, Opioid / Q000378:metabolism; D014020:Tissue Extracts / Q000494:pharmacology; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid; D014020:Tissue Extracts; C033593:methionine-enkephalin receptor; D007987:Gonadotropin-Releasing Hormone; D004744:Enkephalin, Methionine; D001615:beta-Endorphin