αand Luteinizing HormoneβMessenger Ribonucleic Acid (RNA) of Male and Female Rats after Castration: Quantitation Using an Optimized RNA Dot Blot Hybridization Assay*

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Abstract
In this study we examined the changes in .alpha. and LH.beta. mRNAs in anterior pituitaries of male and female rats after castration. mRNA concentrations were measured by the optimized RNA dot blot hybridization assay. Rat .alpha. and LH.beta. cDNAs were nick-translated to specific activities of 2-5 .times. 108 cpm/.mu.g and were used as hybridization probes. The total RNA per assay, RNA per dot, and saturating amounts of probe were optimized. The intra- and interassay coefficients of variation were 5% and 28%, respectively. Both .alpha. and LH.beta. mRNA concentrations increased after castration, but marked differences were observed in the kinetics of responses in male and female rats. In males, .alpha. and LH.beta. mRNAs were increased by 24 h postcastration (by 25% and 38%, respectively), and 4- to 5-fold increases over intact controls were evident by 18 days. .alpha. mRNA rose rapidly and had doubled by 2 days, whereas LH.beta. mRNA concentrations showed a similar increase by 6-7 days postcastration. The slower rise in LH.beta. mRNA was associated with a transient decline in serum and pituitary LH concentrations between 2 and 6 days after castration. In female rats, .alpha. mRNA increased more slowly, .alpha. concentrations had doubled by 10 days, while a similar increase in LH.beta. mRNA occurred 7 days after castration. Thereafter, both subunit mRNAs continued to rise, and by day 20 .alpha. mRNA was increased 5-fold and LH.beta. mRNA 16-fold over values in intact females. Serum and pituitary LH concentrations rose gradually, and both were increased by 7-10 days after castration. The increase in serum and pituitary LH followed a time course similar to that of the progressive rise in LH.beta. mRNA concentrations. These data show that an increase in steady state LH subunit mRNA concentrations is one of the mechanisms involved in increased gonadotropin biosynthesis and secretion after castration. The kinetics of LH subunit mRNA and LH secretory responses are different in male and female rats and suggest that the concentration of LH.beta. mRNA may be a limiting factor in LH secretion.