Ovarian Function in Hamsters Treated with Monosodium Glutamate

Abstract

It is well known that the administration of monosodium glutamate (MSG) in early life will cause disturbances in the reproductive neuroendocrine axis by destroying the neurons in the arcuate nucleus of the hypothalamus. Three experiments were designed to determine whether there is a direct effect of neonatally administered MSG on the function of the ovaries when the animals become adults. Hamsters were injected s.c. with saline or 8 mg MSG/g BW on Day 8 of the neonatal period. All subsequent investigations were performed on groups of 5–7 animals at least 2 months after injection. In experiment 1, the levels of progesterone (P) were measured in the plasma and interstitial tissue. The results showed that there were significantly higher levels of P in both compartments in all MSG treated animals compared with saline injected controls indicating that synthesis and release of P can occur. In experiment 2, the activity of the enzyme 3β-hydroxysteroid dehydrogenase, which is necessary for the synthesis of P, was studied histochemically in the ovaries. Enzyme activity was demonstrable in both control and MSG treated animals. This correlates well with published reports on the hamster since LH from the pituitary is known to stimulate P secretion from the interstitial tissue and the levels of LH in the MSG treated hamster are elevated. In experiment 3, saline treated animals were ovariectomized; they then had ovaries from saline or MSG treated animals transplanted under the kidney capsule and the onset of regular estrous cycles was recorded. All animals that received transplants from either group had 2–4 consecutive estrous cycles and comparable levels of LH and FSH. Histological examination of the transplants revealed that there was maturation of follicles and formation of corpora lutea. This indicated that the ovaries from MSG treated animals were capable of responding to gonadotropin stimulation. Serial sections of the hypothalamus revealed a lesion of the arcuate nucleus in all animals given MSG in all 3 experiments. These results demonstrate that MSG does not have a direct effect on the function of the ovary, at least with the techniques used in this study.