Growth patterns and hormonal profile of male rats with protein-calorie malnutrition

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Abstract
A condition of protein‐calorie malnutrition was precipitated in young Sprague‐Dawley male rats at 20 days of age using an 8% low protein diet (LPD). At five‐day intervals for up to 50 days of age, the rats were studied to determine the effect of an LPD on the reproductive axis of the endocrine system. Daily monitoring of the body weight, as well as the consumption of food, kilocalories, and protein was conducted. The same parameters were followed over the identical time peroid in a group of animals designated as controls which were fed a standard laboratory diet (SLD) containing 27% protein. The controls showed a linear growth rate over the 30‐day experimental period. In comparison, the malnourished rats grew more slowly so that by 50 days of age, their mean body weight was 68.9 ± 3.1 g as compared to 249.1 ± 6.1 g for the controls. The daily food, kilocalorie, and protein intake by the experimental animals were also appreciably less. The pituitary gland, ventral prostate gland, testes and liver were smaller in the animals fed the LPD. This was observed as early as five days after initiating the dietary regimes and remained a consistent observation until the end of the experiment. In general, the absolute weights of these organs in the 50 day‐old malnourished rats were similar to those found in 25 to 26 day‐old animals fed the SLD. The relative weights of the pituitary gland and liver remained similar between the two animal groups. The testes and ventral prostate gland, however, were relatively smaller in the malnourished animals at nearly every time interval studied. On light microscopic examination of the testes, it was found that normal maturation of the germ cells failed to occur in all but one of the experimental animals, whereas maturation proceeded normally in the rats fed the SLD. Serum luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL), and testosterone were lower in the malnourished animals at all ages studied. These hormones did not exhibit the fluctuations that were seen in the controls and are typical in rats that are becoming sexually mature. The effect of protein deficiency on the concentration of the pituitary gonadotrophins was more varied. FSH concentrations were consistently lower, PRL was moderately affected, and LH remained essentially unchanged. Hypothalamic LH‐releasing hormone was measured and found to be significantly less in the rats fed the LPD at most of the time intervals examined. These results indicate that the hypothalamo‐hypophyseal‐gonadal axis is impaired when the consumption of proteins and calories is decreased. The possible involvement of extrahypothalamic centers in the control of hormone secretion in the protein‐deficient rat is discussed.

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