Alpha and luteinizing hormone beta messenger ribonucleic acid (RNA) of male and female rats after castration: quantitation using an optimized RNA dot blot hybridization assay.

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 an optimized RNA dot blot hybridization assay. Rat alpha and LH beta cDNAs were nick-translated to specific activities of 2-5 X 10(8) cpm/micrograms 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.