Tyrosine hydroxylase (TH) in the median eminence (ME) and superior cervical ganglion (SCG) of the rat was quantified by means of an immunoblot procedure, using highly purified rat TH as the standard. Antibodies against rat TH were produced in the rabbit. The assay was linear from 0-100 ng TH and had a correlation coefficient of 0.990 ± 0.0014 (mean ± SE: = 22). The interassay coefficient of variation was 8.65% (n = 17). In young female rats (12-16 weeks old) with regular 4-day estrous cycles, the quantity of TH in the ME oh various days of the cycle was as follows: Estrus, 42 ± 2.9 ng; diestrous day 1, 61 2.8 ng; diestrous day 2, 75 ± 4.2 ng; and proestrus, 84 ± 3.3 ng. In ovariectomized rats (15-16 weeks old), the ME contained 24 ± 1.6 ng TH. In prepubertal rats (5-5.5 weeks old), the ME of females contained 25 ± 2.0 ng TH, and that of males contained 24 ± 2.1 ng. The amount of TH in the ME of young mature males (15-16 weeks old) was 34 ± 3.3 ng, and that of old males 17-20 months old) was 37 ± 1.6 ng TH. In aged female rats 22-24 months old), the Mills of diestrous and estrous animals contained 71 ± 2.8 and 63 ± 4.2 ng TH, respectively. In cycling females (12-16 weeks old), the quantity of TH per SCG was as follows: Estrus, 41 ± 3.2 ng, diestrous day 1,64 ± 1.2 ng; diestrous day 2,82 ± 4.4 ng; and proestrus, 101 ± 4.9 ng. In ovariectomized rats (15-16 weeks old), there was 34 ± 2.0 ng TH/SCG. In prepubertal rats (5-5.5 weeks old), the SCG of females contained 33 ± 4.1 ng TH, and that of males contained 32 ± 2.3 ng. The amount of TH in SCG of mature males (15-16 weeks old) was 47 ± 3.0 ng, and that in old males (17-20 months old) was 58 ± 4.6 ng. In aged female rats (22-24 months old), the SCG of diestrous animals contained 152 ± 6.3 ng TH, and that of constant estrous animals contained 139 ± 8.8 ng TH. It is concluded that before puberty, the amounts of TH in the ME and SCG of female rats are similar to those in male rats. After puberty, the amount of TH in these structures is greater in females than in males. The amount of TH in the ME and SCG varies throughout the estrous cycle, being greatest on proestrus and least on estrus. In aging female rats, there is a marked increase in the amount of TH in the SCG.
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