Gonadotropin and gonadal steroid release in response to a gonadotropin- releasing hormone agonist in G(q)α and G₁₁α knockout mice

In this study, we used mice lacking the G₁₁α [G₁₁ knockout (KO)] or G(q)α gent (G(q) KO) to examine LH release in response to a metabolically stable GnRH agonist (Buserelin). Mice homozygous for the absence of G₁₁α and G(q)α appear to breed normally. Treatment of (5 wk old) female KO mice with the GnRH agonist Buserelin (2 μg/100 μl, sc) resulted in a rapid increase of serum LH levels (reaching 328 ± 58 pg/25 μl for G₁₁ KO; 739 ± 95 pg/25 μl for G(q) KO) at 75 min. Similar treatment of the control strain, 129SvEvTacfBr for G₁₁ KO or the heterozygous mice for G(q) KO, resulted in an increase in serum LH levels (428 ± 57 pg/25 μl for G₁₁ KO; 884 ± 31 pg/25 μl for G(q) KO) at 75 min. Both G₁₁ KO and G(q) KO male mice released LH in response to Buserelin (2 μg/100 μl of vehicle; 363 ± 53 pg/25 μl and 749 ± 50 pg/25 μl 1 h after treatment, respectively). These values were not significantly different from the control strain. In a long-term experiment, Buserelin was administered every 12 h, and LH release was assayed 1 h later. In female G₁₁ KO mice and control strain, serum LH levels reached approximately 500 pg/25 μl within the first hour, then subsided to a steady level (~100 pg/25 μl) for 109 h. In male G₁₁ KO mice and in control strain, elevated LH release lasted for 13 h; however, LH levels in the G₁₁ KO male mice did not reach control levels for approximately 49 h. In a similar experimental protocol, the G(q) KO male mice released less LH (531 ± 95 pg/25 μl) after 13 h from the start of treatment than the heterozygous male mice (865 ± 57 pg/25 μl), hut the female KO mice released more LH (634 ± 56 pg/25 μl) after 1 h from the start of treatment than the heterozygous female mice (346 ± 63 pg/25 μl). However, after the initial LH flare, the LH levels in the heterozygous mice never reached the basal levels achieved by the KO mice. G₁₁ KO mice were less sensitive to low doses (5 ng/per animal) of Buserelin than the respective control mice. Male G₁₁ KO mice produced more testosterone than the control mice after I h of stimulation by 2 μg of Buserelin, whereas there was no significant difference in Buserelin stimulated testosterone levels between G(q) KO and heterozygous control mice. There was no significant difference in Buserelin stimulated estradiol production in the female G(q) KO mice compared with control groups of mice. However, female G₁₁ KO mice produced less estradiol in response to Buserelin (2 μg) compared with control strain. Although there were differences in the dynamics of LH release and steroid production in response to Buserelin treatment compared with control groups of mice, the lack of complete abolition of these processes, such as stimulated LH release, and steroid production, suggests that these G proteins are either not absolutely required or are able to functionally compensate for each other.