Histochemical studies of muscle development in decapitated and hypophysectomized pig fetuses: blood vessel development.

In Exp. 1, fetuses were decapitated in utero on d 45 of gestation and examined at 110 d of gestation; in Exp. 2, fetuses were hypophysectomized (hypox) in utero with a cauterizing needle at d 70 of gestation and examined at 110 d of gestation. Semitendinosus muscles were sampled and transverse cryostat sections were cut from the medial portion of the muscle. Quantitative analysis of lectin-stained sections showed that capillary:fiber ratios (C/F) were lower (P less than .01) for sections from decapitated and hypox fetuses than for sections from control fetuses. The superficial and deep aspects of muscle sections from control fetuses had markedly different C/F ratios (deep region, 24.1 +/- 2; superficial region, 11.2 +/- .5). Fetal decapitation and hypophysectomy abolished differences in C/F ratios between deep and superficial regions of muscle sections (hypox fetuses; deep region, 6.9 +/- 1; superficial region, 6.4 +/- .6). Capillaries in sections from control fetuses were reactive for several enzymes, whereas capillaries in sections from experimental fetuses (decapitated and hypox) were not reactive for these enzymes. The number of small arterioles was reduced in sections from experimental fetuses (decapitated and hypox) compared with sections from control fetuses. These studies demonstrate that lowering the levels of pituitary hormones in the fetus retards the development of blood vessels in muscle tissue both quantitatively and qualitatively.