Effect of the suckling stimulus on daily LH surges induced by chronic oestrogen treatment in ovariectomized lactating rats.
Effects of the suckling stimulus on the daily LH surge induced by chronic oestrogen treatment were examined in ovariectomized lactating rats. Wistar-Imamichi strain rats were kept under 14 h light:10 h darkness (lights on at 05.00 h). Litter size was adjusted to eight on day 1 (day 0 = day of parturition) and ovariectomy performed on day 2. Lactating rats deprived of their litters on day 0 served as nonlactating controls. Silicone elastomer tubing filled with oestradiol was implanted on day 6 or 15. Blood samples were collected through an indwelling cannula at 10.00 and 17.00 h on each day after implantation to detect daily LH surges. Daily LH surges occurred in the late afternoon in both lactating and non-lactating rats implanted with oestradiol on day 6 or 15. The amplitude of daily LH surges in lactating rats implanted on day 6 declined much more rapidly than in non-lactating rats implanted on day 6, but no significant difference was found in the profile of the LH surge between lactating and non-lactating rats implanted on day 15. Pituitary LH contents just before the daily LH surge (12.00-12.30 h) 4 days after implantation in lactating rats implanted with oestradiol on day 6 were significantly less than those in nonlactating rats implanted with oestradiol on day 6 or 15 and in lactating rats implanted on day 15.(ABSTRACT TRUNCATED AT 250 WORDS)
Tsukamura
H
H
Laboratory of Reproductive Physiology, School of Agriculture, Nagoya University, Japan.
Maeda
K I
KI
Yokoyama
A
A
D000818:Animals; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007774:Lactation / Q000097:blood*; D007986:Luteinizing Hormone / Q000097:blood* / Q000378:metabolism; D010052:Ovariectomy; D010902:Pituitary Gland / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D013997:Time Factors
D004958:Estradiol; D007986:Luteinizing Hormone