Pre-pubertal exposure to high temperature impairs ovarian and adrenal gland function in female rats

Abstract

The influence of different levels of heat exposure on the functions of ovarian and adrenal gland were investigated in pre-puberty female rats. Three-week old female rats were treated with control (26°C) or three higher temperatures (38, 40 and 42°C) for 2hr/day. After 9 days of treatment, blood samples were collected for measurement of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol-17β, corticosterone, cholesterol and triglyceride. Adrenal glands, ovaries and liver were collected for analyzing gene expressions. Body and liver weight were significantly low in the 42°C heating group. Circulating LH and triglyceride in the 42°C heating group were significantly lower, and estradiol-17β, corticosterone and cholesterol were significantly higher than those of the control group. The gene expression of 3β-HSD and P450c21 in the adrenal gland; 3β-HSD, receptors of LH, FSH and estrogen in the ovary were significantly low in heated rats. The liver gene expressions of caspase 3 and NK-κB were significantly high in 42°C heated rats, suggesting that the ability of liver metabolic function reduced in the 42°C heated rats. These results demonstrated that the high temperature is responsible for suppression of ovarian function by decreasing the expression of steroidogenic enzymes, estrogen and gonadotropin receptors in the ovary. Increase in circulating estradiol-17β in the heated rats may be due to accumulate this hormone in circulation by potential changes in liver metabolism during the heat stress.

Keywords: corticosterone; estradiol-17β; heat stress; rat; steroidogenesis.

Fig. 1.

Body weight of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 21, 25 and 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control. *P<0.05.

Fig. 2.

The liver weight of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control. **P<0.01.

Fig. 3.

Plasma concentrations of luteinizing hormone (LH; a), follicle-stimulating hormone (FSH; b), estradiol-17β (c), corticosterone (d) and cholesterol (e) of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats except 40°C treated rats in the panel a (n=2). Asterisks indicate significant difference compared to the control. *P<0.05; **P<0.01.

Fig. 4.

The gene expression of StAR (a) steroidogenic enzymes P450scc (b), 3β-HSD (c) and P450c21 (d) in the adrenal gland of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control (*P<0.05 and **P<0.01).

Fig. 5.

The gene expression of StAR (a) steroidogenic enzymes 3β-HSD (b) and CYP17α (c) in the ovary of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control (*P<0.05 and **P<0.01).

Fig. 6.

The gene expression of receptor of LH (LHR: a), FSH (FSHR: b) and estrogen (ER: c) in the ovary of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control (*P<0.05 and **P<0.01).

Fig. 7.

The gene expression of Caspase 3 (a) and NK-κB (b) in liver of control (26°C) and heat treated immature female rats (38, 40, 42°C) at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control (*P<0.05).

Fig. 8.

Plasma concentrations of triglyceride in the 26°C control rats and the 42°C heat treated rats at 30 day of age. Each bar represents mean ± S.E.M. of 4 rats. Asterisks indicate significant difference compared to the control (*P<0.05).