Summary. Six lactating sows were injected through an indwelling vena cava cannula with naloxone (2·5 mg/kg body weight) on Day 15 post partum. Blood samples were collected through the cannulas at 10-min intervals for 8 h before and 10 h after naloxone administration. Plasma prolactin and LH concentrations were measured by radioimmunoassay. Naloxone caused a marked suppression of plasma prolactin concentrations lasting 4–6 h. LH concentrations were also affected by naloxone: LH rose to reach maximum values 20–50 min after naloxone treatment. Pretreatment values were recorded 200–300 min after the treatment. These results indicate that endogenous opioids are involved in causing the endocrine patterns occurring during lactation, i.e. high prolactin and low LH concentrations.
M. Mattioli, F. Conte, Giovanna Galeati, and E. Seren
Rosella Gaiani, F. Chiesa, M. Mattioli, G. Nannetti, and Giovanna Galeati
Summary. Androstenedione concentrations in both plasma and milk were higher than those of testosterone throughout pregnancy. Testosterone concentration increased during pregnancy; the levels in milk were always lower than in plasma. Androstenedione concentrations increased in plasma and milk during pregnancy but the values were twice as high in milk as in plasma after Day 90. This change in androstenedione distribution suggests that the mammary gland could be active in the uptake of androstenedione from plasma to milk or that the mammary gland itself might synthesize this hormone.