Prepartum, multiparous ewes were randomly assigned to
experimental groups and sacrificed at 50(n=5), SO(n=4),115(n=5), and 140(n=4) days of gestation. Serum harvested
the week prior to slaughter was assayed for progesterone
(PG), prolactin (PRL) and growth hormone (GH)
concentrations. Mammary tissue obtained at slaughter was
assayed for receptor concentrations of progesterone (PGr),
prolactin (PRLr) and insulin (Ir). Quantitative
biochemical, histological and autoradiographical analyses
were used to measure mammary gland growth and indicated no
significant glandular growth occurs prior to 8O days of
gestation. However, a major phase of parenchymal growth
occurred between 8O and 115 days which coincided with
significant increases in PG, PGr and PRLr concentrations.
Parenchymal growth continued further into late pregnancy.
GH and Ir concentrations did not change significantly during
pregnancy and were not strongly correlated to growth
measurements. These results suggest that mammary gland
growth is receptor-mediated and direct or indirect
regulation of PGr and PRLr is primarily responsible for the
observed growth phenomenon.
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