Quantitative Histochemical Studies of the Hypothalamus. Control Point Enzymes during the Estrous Cycle

Abstract

Three control point enzymes of the Embden-Meyerhof pathway, hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK), have been measured in individual hypothalamic nuclei during the 5-day estrous cycle of adult rats by quantitative histochemical methods. PK levels, low during proestrus, rise to maximum activity during estrus; this rise is significantly greater than on all other days of the cycle in the lateral preoptic area (LP), ventromedial pars medialis (VMM) and pars lateralis (VML) and posterior hypothalamic (Post) nuclei. HK activity also rises from low proestrous levels during the cycle but, in contrast to PK, reaches maximum activity during diestrus-1 (D-l) or diestrus-2 (D-2). PFK showed variable changes during the estrous cycle with peaks occurring during estrus in some nuclei and during diestrus in others, but these changes were not significantly different. These metabolic changes occur in specific hypothalamic nuclei which have been shown by electrical stimulation, lesion production, stereotaxic hormone implantation and localization of luteinizing hormone-releasing factor experiments to have an important role in reproductive physiology and sexual behavior.

Quantitative Histochemical Studies of the Hypothalamus: Dehydrogenase Enzymes following Androgen Sterilization

“…The specific procedures used to obtain samples of individual hypothalamic nuclei examined in this study have been described previously [Packman et at., 1976]. The measurement of enzyme activity is based on the formation of a fluorescent product of the oxidized pyridine nucleotide in a strongly alkaline solution [Lowry et at., 1957], The specific assay conditions for MDH, LDH and G-6-PDH have been described [Packman et at., 1977], The GDH assay system coniained the following, in nmoles. in a total volume of 5 p\: Tris buffer, pH 7.6, 500; NADH, 2.0; cx-ketoglutarate, 16.1; ammonium acetate, 515; ADP, 5.9; sodium amytal.…”

Quantitative Histochemical Studies of the Hypothalamus. Control Point Enzymes Following Androgen Sterilization

“…The procedures for obtaining the individual hypothalamic nuclear samples examined in this study have been described [Packman et a!., 1977c]. The measurement of HK, PFK, and PK was carried out through use of coupled enzyme assay systems in order to obtain an oxidized pyridine nucleotide which forms a fluorescent product in strong alkali [Lowry et al, 1957].…”

“…The measurement of HK, PFK, and PK was carried out through use of coupled enzyme assay systems in order to obtain an oxidized pyridine nucleotide which forms a fluorescent product in strong alkali [Lowry et al, 1957]. The specific conditions for enzyme assays measured in the present study have been described in detail [Packman et al, 1977c], Lipid-free dry weights [Lowry, 1953] were determined for each area.…”