Growth and Development of the Neonatal Rat: Particular Vulnerability of Males to Disadvantageous Conditions during Rearing

Abstract

Rat pups were nurtured on radioactive iodine-containing milk by dams fed low-iodine (Remington) diets plus sodium ¹²⁵I-iodide (Na ¹²⁵I) supplements from 3 days before parturition to the time of weaning. Effects of individual features of this experimental regimen on developmental progress of the offspring were examined. Nutritional deficiencies inherent in the maternal Remington diet did not alter growth rate, if the pups were only minimally disturbed in the course of rearing. However, when combined with chronic handling stress (itself having no detectable effect on the weight gain of pups of normally fed mothers), growth retardation was noted, without evidence of hypothyroidism. Addition of Na ¹²⁵I to the maternal Remington diet reduced the growth rate of non-handled animals only. The strategy of measuring post-weaning catch-up growth served to magnify latent signs of pre-weaning growth retardation and revealed that males were more susceptible than females to early dietary deficiencies, radiation and handling stresses.