ABSTRACT
The purpose of this study was to determine the effects of nitrate on both the activity of the thyroid gland and other biological parameters. After 5-month treatment, nitrate 150 and 500 mg/l induced a significant decrease in the serum level of thyroid hormone T3. For T4, the 500 mg/l dose only reduced its plasma level. On the other hand, nitrate induced a dose-dependent increase in the weight of the thyroid gland. The histological study of the thyroid gland shows vacuolisation and an increase in the size of the follicles accompanied by a flatness of follicular epithelium with nitrate 150 and 500 mg/l. We concluded that the presence of high concentrations of nitrate in drinking water influence the growth, induce morpho-functional modifications of the thyroid gland and might be considered as a goitrigenic factor.
Subject(s)
Nitrates/toxicity , Potassium Compounds/toxicity , Thyroid Gland/drug effects , Water Pollutants/toxicity , Administration, Oral , Animals , Dose-Response Relationship, Drug , Drinking , Male , Morocco , Nitrates/administration & dosage , Potassium Compounds/administration & dosage , Rats , Rats, Wistar , Thyroid Gland/metabolism , Thyroid Gland/pathology , Thyroxine/blood , Triiodothyronine/blood , Water Pollutants/administration & dosage , Water Supply/analysisABSTRACT
Age related changes in the time courses of response of plasma corticosterone and aldosterone to exogenously applied ACTH were simultaneously studied in old (female and male) Long-Evans rats and compared to both young and adult pentobarbitone-anesthetized and dexamethasone-pretreated control rats. Acute intravenous injection of either 0.5 or 50.0 ng ACTH (1-24)/100 g body weight increased plasma concentrations of the two steroids with a similar time course in all groups of rats. However, we observed a significant age-related attenuation in the plasma corticosteroid response. Thus, in old as compared to young rats there was a decrease of approximately 45, 40 and 30% in plasma corticosterone levels respectively 8 min after the lower dose of ACTH in female and 45 min after the higher dose in female and male rats. Similarly, an attenuated (approximately -38%) response of plasma aldosterone levels, induced 45 min after the higher dose of ACTH, was observed both in old female and male rats. These results suggest that the previously reported age-related decreases of in vivo corticosterone and aldosterone secretion are, at least in part, due to a reduced capacity of adrenocortical cells for steroid biosynthesis and release in response to stimulation by ACTH.
Subject(s)
Aging/blood , Aldosterone/blood , Corticosterone/blood , Cosyntropin/pharmacology , Animals , Female , Male , Rats , Rats, Inbred Strains , Time FactorsABSTRACT
Age-related changes in plasma adrenocorticotropic hormone (ACTH), corticosterone, and aldosterone responses to exogenous corticotropin-releasing hormone (CRH) were studied concomitantly in both old and adult Long-Evans female rats. All animals were pretreated with dexamethasone and pentobarbital anesthetized. An acute intravenous injection of 1 micrograms rat CRH/100 g body weight markedly increased the plasma concentrations of ACTH, corticosterone, and aldosterone--with similar temporal kinetics in the two groups of rats. However, the incremental CRH responses were significantly lower in old (approximately -70, -45-60, and -30-50%, respectively, for ACTH, corticosterone, and aldosterone) as compared with adult rats. Together with our recent findings, the present results suggest that the previously reported reduced secretion of corticosteroids in aged rats is due to both an impaired steroidogenetic capacity of adrenocortical cells to respond to ACTH and to a decreased ability of corticotropes to produce ACTH in response to CRH.
