Summary
Individual rabbit fetuses in utero were injected intramuscularly with either 2.0 Units protamine zinc insulin or saline
at 23 days gestation after surgical reduction of litter size to 4 fetuses at 9 days
gestation. Insulin-treated fetuses were still hyperinsulinaemic compared with littermate
controls at 28 days gestation. Neither fetal body weight nor carcase composition were
affected by insulin injection, but placental weight and RNA content were increased.
Placental weight was highly correlated with plasma insulin concentration in control
fetuses, but not in insulin-injected fetuses.
Twenty-four hours after injection of insulin into individual fetal rabbits from normal
litters at 23 or 27 days gestation insulin-injected fetuses were hyperinsulinaemic
and euglycaemic, but had significantly higher plasma glucocorticoid concentrations
than saline-injected littermates.
Stimulation of placental growth by fetal insulin may be an important component of
the fetal growth stimulatory effect of endogenous insulin. Growth stimulatory effects
of exogenous insulin may be antagonised by raised plasma glucocorticoid concentrations.
Key-Words
Rabbit Fetus
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Insulin
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Growth
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Placenta
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Glucocorticoids
