Neuroendocrine aspects of aging in women.

In women, the loss of ovarian function at menopause is associated with marked changes in hypothalamic and pituitary function. In addition, the steady decline in serum levels of LH, FSH, and FAS with age following menopause provides clear evidence for age-related neuroendocrine changes independent of the changes occurring owing to loss of ovarian feedback on the hypothalamic and pituitary components of the reproductive axis. An increase in the overall amount of GnRH secreted occurs despite a 30% decrease in GnRH pulse frequency with aging. This observation implies that the amount of GnRH secreted with each secretory bolus is greater in older postmenopausal women when compared with younger postmenopausal women. Thus, there may be a prominent pituitary component to the age-related decline in gonadotropin secretion. Recent studies indicate that the response to estrogen negative feedback at the hypothalamic level is preserved with aging, whereas the response to estrogen positive feedback may decrease with reproductive aging; however, the response to estrogen positive feedback in women has not been investigated with respect to aging, per se. It will be important to determine whether these age-related changes in hypothalamic-pituitary function contribute to reproductive senescence in normal women, as has been suggested for similar changes in animal models.

Insights into hypothalamic-pituitary dysfunction in polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is characterized by menstrual dysfunction and hyperandrogenism in the absence of other known causes. While the pathogenesis of PCOS remains elusive and is likely to involve abnormalities in several systems, there has long been an association of abnormal gonadotropin secretion with this disorder. In recent studies we have determined that 94% of women meeting the broad criteria for PCOS have an increased LH/FSH ratio. Several lines of evidence suggest that the mechanisms underlying the increased LH/FSH ratio in PCOS include an increased frequency of GnRH secretion. Decreased sensitivity to progesterone negative feedback on the GnRH pulse generator may play a role in this neuroendocrine defect. Additional factors which may contribute to the low to normal FSH levels in the face of increased LH include chronic mild estrogen increases and possibly inhibin. In addition to these effects on the differential control of FSH, there is increased pituitary sensitivity of LH secretion to GnRH. Both estrogen and androgens have been proposed as candidates mediating these effects. Superimposed on these underlying abnormalities in gonadotropin secretion is a marked inhibitory effect of obesity on LH secretion which may be mediated at either a pituitary or hypothalamic level.

Extended aromatic furan amidino derivatives as anti-Pneumocystis carinii agents.

The syntheses of nine new derivatives of 2, 5-bis[4-(N-alkylamidino)phenyl]furans with extended aromatic systems are reported. The interaction of these dicationic furans with poly(dA)poly(dT) and with the duplex oligomers d(CGCGAATTCGCG)2 and d(GCGAATTCGC)2 was determined by Tm measurement, and the effectiveness of these compounds against the immunosuppressed rat model of Pneumocystis carinii was evaluated. At a screening dose of 10 micromol/kg, 4 of the 12 amidino furans described here are more active than the parent compound 1. In general, extension of the aromatic system in the absence of a substitution of the amidino nitrogens resulted in higher affinity for DNA than the parent compound as judged by the larger DeltaTm values and suggests enhanced van der Waals interactions in the amidino furan-DNA complex. Three of the compounds, 3, 5, and 11, yield cysts counts of less than 0.1% of control when administered at a dosage of 10 micromol/kg. Compound 3, which does not have an extended aromatic system, is the most active derivative. Although a direct correlation between anti-P. carinii activity and DNA binding affinity was not observed, all compounds which have significant activity have large DeltaTm values.

1,5-Bis(4-amidinophenoxy)pentane (pentamidine) is a potent inhibitor of [3H]idazoxan binding to imidazoline I2 binding sites.

The aromatic diamidine 1,5-bis(4-amidinophenoxy)pentane (pentamidine) is used for treatment and prophylaxis of Pneumocystis carinii pneumonia in patients with Acquired Immune Deficiency Syndrome. Clinical use of pentamidine has been restricted by significant toxicity, that includes hypotension, and hypoglycemia. Although clinical toxicity is well described, the mechanisms are still poorly understood. Competitive binding analyses using [3H]idazoxan as the radioligand, and cirazoline to define non-specific binding, demonstrate that pentamidine binds to an imidazoline I2 binding site on rat liver membranes with a Ki of 1.4+/-0.22 nM. The Ki indicates that pentamidine inhibits radioligand binding at imidazoline I2 sites with an affinity approximating the most potent known ligands and may be related to pentamidine toxicity. Moreover, pentamidine analogs inhibit radioligand binding with a range of affinities that vary according to their structure. Two candidate drugs, Compounds 5 and 6, are more active than pentamidine in the corticosteroid-suppressed rat model of P. carinii pneumonia, yet have different affinities for the imidazoline I2 site (Ki 5 = 50.1+/-1.06 nM and Ki 6 = approximately 3500 nM). Affinity for this site does not correlate with antimicrobial activity (r = 0.60; p = 0.09) or the calculated log of the octanol:water partition coefficient (ClogP) (r = -0.38; p = 0.22).

Potential for fertility with replacement of hypothalamic gonadotropin-releasing hormone in long term female survivors of cranial tumors.

Dysfunction of the hypothalamic-pituitary axis presenting as hypogonadotropic amenorrhea is a common sequelae of treatment for cranial tumors with surgery and/or radiation. We hypothesized that the site of the defect in this condition is hypothalamic, rather than pituitary, in the majority of patients. Nine women with acquired hypogonadotropic hypogonadism after treatment with transphenoidal pituitary surgery (n = 3), transphenoidal surgery plus conventional radiotherapy (XRT; n = 1), hypothalamic surgery plus XRT (n = 2), or XRT with or without noncentral nervous system surgery (n = 3) underwent assessment of endogenous pulsatile LH secretion and a standard GnRH test followed by iv administration of a physiological replacement regimen of exogenous GnRH. A total of 25 cycles were completed at doses of 75 or 100 ng/kg.bolus. Ovulation occurred in 78% of patients, with all ovulatory patients who desired fertility becoming pregnant. The hormonal responses in these cycles did not differ from the patterns of sex steroids and gonadotropins in normal women. The response to pulsatile GnRH was not influenced by GH deficiency or PRL abnormalities. Of the two patients who failed to ovulate, there was no evidence of folliculogenesis in one, whereas the second consistently developed follicles, but proved incapable of mounting a LH surge despite adequate preovulatory estradiol levels. Both patients had a history of pituitary radiation and surgery. There was no consistent relationship between the results of GnRH testing and the pattern of pulsatile LH secretion. However, the only patient who failed to achieve folliculogenesis was the only patient without a FSH response to GnRH testing and an apulsatile baseline study. Hypothalamic GnRH deficiency is the etiology of hypogonadism in the majority of patients after treatment with hypothalamic or pituitary surgery or cranial irradiation. Therefore, exogenous pulsatile GnRH represents a physiological replacement therapy that completely restores normal gonadotropin dynamics, resulting in ovulation and fertility.

In vitro tryptophan catabolism by Leishmania donovani donovani promastigotes.

Metabolism of tryptophan by promastigotes of Leishmania donovani donovani was investigated in cells suspended in a simple buffer solution supplemented with glucose. Metabolites from supernatant and lysed cell pellets were analyzed by capillary gas liquid chromatography and 13C nuclear magnetic resonance spectroscopy, with structural confirmation by gas liquid chromatography-mass spectrometry. Tryptophan does not appear to serve as a carbon energy source for L. d. donovani promastigotes since parasites could survive for only short periods in buffer containing tryptophan without glucose, levels of tricarboxylic acid cycle intermediates remained unchanged in the presence of added tryptophan and label from [13C]tryptophan was not detected in any of the intermediates. Leishmania d. donovani catabolized L-tryptophan via aminotransferase and aromatic lactate dehydrogenase reactions to form one major end product, indole-3-lactic acid. The activity of aromatic lactate dehydrogenase required manganese and was NADH-dependent in these organisms that lack lactate dehydrogenase. Promastigotes taken from the mid-log stage of growth produced higher concentrations of indole-3-lactic acid than those from the stationary stage. Conservation of a similar tryptophan catabolic pathway among four Leishmania species suggests the pathway is physiologically important to the parasites themselves.

Hypothalamic gonadotropin-releasing hormone secretion and follicle-stimulating hormone dynamics during the luteal-follicular transition.

To define the precise neuroendocrine characteristics of the luteal-follicular transition, 11 normal women underwent 12 frequent sampling studies at 10-min intervals for 48 h at various points during the transition from one cycle to the next. Daily blood samples captured both the preceding and subsequent LH surges, so that studies could be characterized in relation to the preceding LH peak (LH+), the subsequent LH peak (LH-), and menses (M). In the frequent sampling study, LH and FSH were measured in all samples, and estradiol (E2) and progesterone (P) were measured in 2-h pools. The frequency of pulsatile LH secretion increased 4.5-fold over an 8-day period spanning the luteal-follicular transition. This increase in LH pulse frequency was strongly related to the preceding LH peak (r = 0.82; P less than 0.00001), but was not at all related to the onset of menses. When the temporal markers (i.e. LH+, LH-, and M) were removed from the analysis, LH pulse frequency was inversely related to the log of serum P (r = 0.50; P less than 0.005), but not E2. FSH levels increased both within the individual studies (P less than 0.005) and in the group as a whole over the duration of the luteal-follicular transition. Mean FSH rose 3.5-fold compared to less than a 2-fold increase in mean LH. As with LH pulse frequency, the increase in FSH was most strongly related to the preceding LH peak, but was also significantly associated with the subsequent LH peak and the onset of menses. The relationship between FSH and the number of days from the preceding LH peak is even better fit by a second degree polynomial, which revealed an abrupt increase in LH beginning at LH+11. With the temporal markers excluded, the increase in FSH related only to LH pulse frequency (r = 0.62; P less than 0.001). FSH was not statistically related to the decreases in P or E2, which are also key variables at this stage of the menstrual cycle. We reached the following conclusions. 1) A dramatic increase in LH pulse frequency, and by inference GnRH pulse frequency, accompanies the selective rise in FSH levels during the luteal-follicular transition of the normal menstrual cycle. 2) Both the increase in GnRH pulse frequency and the rise in FSH levels during this transition are strongly related to the preceding LH peak, while the clinical marker of menses is a relatively poor indicator of these events.(ABSTRACT TRUNCATED AT 400 WORDS)

Hyperfunction of the hypothalamic-pituitary axis in women with polycystic ovarian disease: indirect evidence for partial gonadotroph desensitization.

To examine gonadotropin secretory frequency as a component of the disordered neuroendocrine regulation of gonadotropin secretion in women with polycystic ovarian disease (PCOD), we measured serum gonadotropin concentrations in 12 women with PCOD at 10-min intervals for periods of 12-24 h. The patterns of LH and FSH release in these patients were compared to the findings of 24 studies in 21 age-matched normal women during the early, mid- and late follicular phases (EFP, MFP and LFP) of their cycles. Serum sex steroid levels during the 12-24 h of study in the women with PCOD were compared to those in normal women studied during the follicular phase. The mean serum estradiol (E2) level in the women with PCOD was similar to that in normal women studied in the EFP, but lower than those in normal women in the MFP (P less than 0.05) and LFP (P less than 0.01). Mean serum estrone, however, was significantly higher in women with PCOD than in women in the EFP and MFP (P less than 0.05 and P less than 0.02, respectively), but lower than that in women in the LFP (P less than 0.02). Total and unbound testosterone (T) levels were significantly elevated in women with PCOD compared to those in normal women at all stages of the follicular phase (P less than 0.001). The mean serum LH concentration and LH pulse amplitude were markedly elevated in the women with PCOD compared to normal women at all three stages of the follicular phase (P less than 0.05 or less). In addition, LH pulse frequency was faster in women with PCOD [24.8 +/- 0.9 ( +/- SE) pulses/24 h] than that in women in the EFP (15.6 +/- 0.7; P less than 0.01), MFP (22.2 +/- 1.1; P less than 0.05) and LFP (20.8 +/- 1.2; P less than 0.01). This increased LH pulse frequency in women with PCOD correlated with ambient serum E2 levels on the day of study (r = 0.84; P less than 0.001), but not with serum estrone, T, or unbound T. Repeat studies in four women with PCOD demonstrated a similarly abnormal gonadotropin secretory pattern in each. We conclude that 1) women with PCOD have an increase in both the amplitude and frequency of LH secretion compared to those in normally cycling women throughout the follicular phase; 2) the defect in women with PCOD is reproducible.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood metabolic profiles: their use and relation to nutritional status of dairy cows.

Profiles of blood metabolites have been used widely to identify problem herds and to indicate dietary causes of disease or low production. Related herd survey studies and designed experiments are reviewed. An initial study of profiles and estimated nutrient intake of five "normal" and four "problem" herds was conducted between 1972 and 1974 to establish baseline values for blood metabolites. Profiles of blood metabolites for additional problem herds were obtained during 1974 through 1977. Variation due to herd of origin, production, stage of lactation, and season of year are important causes of variation in concentrations of metabolites in jugular blood of dairy cows. They need to be considered carefully in interpreting profiles of blood metabolites. Several relationships between dietary intake of nutrients and concentrations of associated components in jugular blood are significant. Concentrations of metabolites are of almost no practical use for individual cows because of extreme variations in diet required to generate abnormal concentrations of blood metabolites. Averages of glucose of blood and nitrogen in urea on seven to ten cows, adjusted for the factors mentioned above, have limited practical value in detecting inadequate energy and protein intake, respectively.