Hormonal profile and reproductive performance in hypoprolactinemic (OFA hr/hr) and normal (Sprague Dawley) female rats

VALDEZ, S.R.; PENISSI, A.; DEIS, R.P.; JAHN, G.A.

REPRODUCTION

Bioscientifica

Lugar: Bristol; Año: 2007 vol. 133 p. 825 - 837

1470-1626

Lactation deficiency may have important consequences on infant health, particularly in populations of low socioeconomic status. The OFA hr/hr strain of rats, derived from Sprague Dawley rats, has deficient lactation and is a good model of lactation failure. We examined the reproductive performance and hormonal profiles in OFA and Sprague Dawley strains to determine the cause(s) of the lactation failure of the OFA strain. We measured hormonal (PRL, GH, gonadotropins, oxytocin and Progesterone) levels by RIA in cycling, pregnant and lactating rats and in response to suckling. Dopaminergic metabolism was assessed by determination of mediobasal hypthalamic dopamine and DOPAC concentrations by HPLC and tyrosine hydroxylase expression by immunocytochemistry and Western blot. OFA rats have normal fertility but 50 % of the litters die of malnutrition on early lactation; only 6 % of the mothers show normal lactation. The OFA rats showed lower circulating PRL during lactation, increased hypothalamic dopamine and DOPAC and impaired milk ejection with decreased PRL and oxytocin response to suckling. Before parturition, PRL release and lactogenesis were normal, but dopaminergic metabolism was altered, suggesting activation of the dopaminergic system in OFA but not in Sprague Dawley rats. The number of arcuate and periventricular neurons expressing tyrosine hydroxylase was higher in Sprague Dawley rats, but hypothalamic expression of TH was higher in OFA rats at the end of pregnancy and early lactation. These results suggest that the OFA rats have impaired PRL release linked with an augmented dopaminergic tone that could be partially responsible for the lactational failure.