Effect of Propylthiouracil-Induced Hypothyroidism on Serum Levels of Luteinizing Hormone and Folliclestimulating Hormone in the Rat

Abstract

It has been reported that thyroxine (T4) influences the production and release of gonadotrophins (Contopoulos, Simpson & Koneff, 1958;Contopoulos & Koneff, 1963;Hagino, 1971). No data are available on the circulating levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in hypothyroid rats. The present study was undertaken to investigate the effects of propylthiouracil (PTU)-induced hypothyroidism on serum LH and FSH levels in male and female rats.Eighteen male and 18 female CD rats (Charles River Breeding Lab.) were divided into three equal groups for each sex and maintained in an air-conditioned and lightcontrolled room with 14 h light/day. They had access to Agway Charles River Formula diet and tap water ad libitum. Group I served as the control receiving vehicle only. Group II were fed PTU (Nutritional Biochemicals) by a stomach tube (5 mg/100 g body wt daily) and were injected with T4 (synthetic, Flint Laboratories) s.c. (2\m=.\5 \g=m\g/100g body wt/day). Group III received the same dose of PTU, but no T4. Treatment was started when the rats were 26 days old and continued for 70 days. Body weights of all rats were recorded weekly. The regularity of oestrous cycles of the female rats was determined by vaginal smears each morning. Blood samples were obtained by cardiac puncture under ether anaesthesia. Samples from females were collected at 14.00 h on the days they exhibited dioestrous vaginal smears. All blood samples were immediately centrifuged and serum kept frozen for the assays. Pituitary, thyroid, adrenals, testes, seminal vesicles, prostates, ovaries and uteri were dissected out, cleaned and weighed on a Roller-Smith torsion balance.Rat serum LH and FSH radioimmunoassay systems distributed by NIAMD, NIH were used as described by Daane & Parlow (1971). Results are expressed in terms of NIAMD-Rat-LH RP-1 standard for LH and NIAMD-Rat-FSH RP-1 for FSH. The data were analysed by analysis of variance and Student's i-test.In our study, 70 days of treatment with PTU had different results in male and female rats, indicating a possible sex difference in gonadotrophin secretion during hypothyroidism (Table 1). Chronic hypothyroidism had a pronounced effect on the oestrous cycles. The cycles were irregular with predominant dioestrous smears. Injection of 2-5 fig T4/100 g body wt/day prevented this effect.

Influence of Thiouracil-induced Hypothyroidism on Adrenal and Gonadal Functions in Adult Female Rats.

“…These findings suggest that hypothyroidism interferes with follicular maturation and results in a decrease in plasma concentrations of estradiol. Previous reports also have shown that hypothyroidism caused a decrease in ovarian weight [1,22,24] and inhibited follicular maturation [22,24]. Hypothyroidism is also known to inhibit FSH-induced aromatase activity of cultured porcine granulosa cells [18].…”

“…The increased plasma concentrations of progesterone is probably due to hypersecretion of PRL during the day of proestrus and estrus. Baksi [1] and Mattheiji et al [19] also have shown that hypothyroidism caused irregular estrous cycles in adult female rats, though they have not mentioned the relationship among hyperprolactinemia, hypersecretion of progesterone and irregular estrous cycles in adult female hypothyroid rats. Previous reports regarding the effects of hypothyroidism on PRL secretion in female rats are conflicting and no study regarding to PRL secretion in hypothyroid adult female rats throughout estrous cycle.…”

“…The lack of thyroid hormone has been known to produce reproductive abnormalities, including irregular menstrual or estrous cycle, amenorrhea and sterility in many species of female mammals [1,9,10,19,24,31]. Thyroidectomy has been reported to cause decreased basal plasma levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH), and a smaller LH surge on the day of proestrus [2,4,29].…”

Is the infertility in hypothyroidism mainly due to ovarian or pituitary functional changes?

“…The data about gonadotropin secretion in hypothyroidism are still controversial (24)(25)(26)(27)(28), with reports of increased, decreased and normal serum levels. Ortega et al (3) suggested a reversal to prepubertal reproductive function in adult rats turned hypothyroid based on the secretion of FSH, LH and estradiol under basal and GnRH-stimulated conditions.…”

Effects of exercise upon circulating thyroxine serum and hepatic lipid concentrations, heart, and seminal vesicles in rats and of age and exercise upon circulating thyroxine in humans

“…Baksi (1973) examined the levels of circulating LH and FSH in propylthiouracil (PTU)-induced hypothyroidism in rats of both sexes. In the females there was no significant reduction in gonadotrophins.…”