Age-related differences in the spontaneous and thyrotropin-releasing hormone-stimulated release of prolactin and thyrotropin in ovariectomized rats.
Effect of estradiol on the spontaneous and thyrotropin-releasing hormone (TRH)-stimulated release of prolactin (PRL) and thyrotropin (TSH) in young and aged ovariectomized (Ovx) rats was investigated. Old (22-26 months) and young (3 months) female rats were Ovx 3 weeks before use. They were injected subcutaneously with estradiol benzoate (EB, 25 micrograms/kg) or sesame oil for 3 days and were catheterized via the right jugular vein. Twenty hours after the last administration of EB, rats were injected with TRH (10 micrograms/kg) through the catheter. Blood samples were collected before and 5, 10, 20, 40 and 60 min after TRH injection. On the day following blood sampling, all rats were decapitated. The anterior pituitary glands (APs) were excised, and incubated with or without TRH (10 ng/ml) at 37 degrees C for 30 min. The basal level of PRL concentration in plasma samples was 5-fold higher in old Ovx rats than in young Ovx rats. Five min after TRH injection, the increase in plasma PRL was greater in old animals than in young animals. Plasma PRL remained higher in old animals than in young animals at 10, 20, 40 and 60 min following TRH challenge. Administration of EB to old and to young Ovx rats produced increases in both basal and TRH-stimulated secretions of PRL, but did not affect the difference in plasma PRL patterns between old and young animals. The release of PRL from APs was increased significantly in all rats after a 30-min incubation with TRH. In Ovx rats injected with oil, the basal release of PRL in vitro was increased with age.(ABSTRACT TRUNCATED AT 250 WORDS)
Wang
P S
PS
Department of Physiology, National Yang-Ming Medical College, Taipei, Taiwan, Republic of China.
Liu
J Y
JY
Hwang
C Y
CY
Hwang
C
C
Day
C H
CH
Chang
C H
CH
Pu
H F
HF
Pan
J T
JT
D000367:Age Factors; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000008:administration & dosage; D005260:Female; D010052:Ovariectomy; D011388:Prolactin / Q000097:blood*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013972:Thyrotropin / Q000097:blood*; D013973:Thyrotropin-Releasing Hormone / Q000008:administration & dosage* / Q000494:pharmacology
D004958:Estradiol; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D013972:Thyrotropin