Donald R. Koritnik

Inhibition of coronary artery atherosclerosis by 17-beta estradiol in ovariectomized monkeys. Lack of an effect of added progesterone.

Although controversy continues, the preponderance of evidence indicates that estrogen replacement therapy favorably influences the risk of coronary heart disease in postmenopausal women. It remains uncertain how this effect is mediated and whether the cyclic addition of a progestin may influence adversely an estrogen-related cardioprotective effect. We investigated the influence of sex hormone replacement therapy on diet-induced coronary artery atherosclerosis in estrogen-deficient (ovariectomized) adult female cynomolgus monkeys. Monkeys were assigned randomly to one of three treatment groups: 1) no hormone replacement (n = 17), 2) continuously administered 17-beta estradiol plus cyclically administered progesterone (n = 20), and 3) continuously administered 17-beta estradiol (n = 18). The physiologic patterns of plasma estradiol and progesterone concentrations were maintained by administering the hormones in sustained-release subcutaneous Silastic implants. The experiment lasted 30 months. At necropsy, coronary artery atherosclerosis was inhibited similarly (reduced by approximately one-half) in animals in both hormone replacement groups (p less than or equal to 0.05). Antiatherogenic effects of hormone replacement were independent of variation in total plasma cholesterol, lipoprotein cholesterol, apoprotein A-1 and B concentrations, high density lipoprotein subfraction heterogeneity, and low density lipoprotein molecular weight. We conclude that physiologic estrogen replacement therapy with or without added progesterone inhibits atherosclerosis progression in ovariectomized monkeys. This may explain why estrogen replacement therapy results in reduced risk of coronary heart disease in postmenopausal women.

Contraceptive steroids and coronary artery atherosclerosis in cynomolgus macaques

The influence of two types of steroidal contraception on the extent of coronary, aortic, carotid, and iliaco-femoral atherosclerosis was assessed in 57 cynomolgus macaques with moderate diet-induced hyperlipoproteinemia. Thirteen animals were treated with an intravaginal ring that released 17 beta-estradiol and levonorgestrel. Fifteen females were treated with an oral contraceptive (OC) composed of ethinyl estradiol and norgestrel. Fifteen females received placebo vaginal rings, and 14 males were untreated. The contraceptive treatments resulted in similar large reductions in plasma high-density lipoprotein (HDL) cholesterol concentrations. Neither treatment influenced the prevalence of coronary artery atherosclerosis. However, treatment with the contraceptive vaginal ring was associated with increased extent of coronary artery atherosclerosis (plaque size) relative to untreated females, whereas treatment with the OC was not. The contrasting effects of the two treatments could not be explained by differences in total plasma cholesterol, HDL cholesterol, or blood pressure. The results suggest that the greater estrogenic influence associated with the ethinyl estradiol-containing OC resulted in inhibition of coronary artery atherosclerosis despite a pronounced progestin-induced lowering of plasma HDL cholesterol concentration and, further, that hormonal balance may have a marked influence on the relationship between plasma lipids and atherogenesis.

Effects of ovariectomy on vertebral trabecular bone in the cynomolgus monkey (Macaca fascicularis)

SummarySeventeen ovariectomized and twenty-one intact female cynomolgus macaques were examined for differences in vertebral trabecular bone volume. The ovariectomized group exhibited significantly less trabecular bone than the intact group (p<.005), 22 months post-ovariectomy. This finding encourages the use of the cynomolgus monkey as a model for the mechanism of bone loss in ovariectomy or postmenopausal osteoporosis.

Pregnancy-associated inhibition of coronary artery atherosclerosis in monkeys. Evidence of a relationship with endogenous estrogen.

We investigated the Influence of repeated pregnancy on diet-Induced atherosclerosis In cynomolgus monkeys and sought to determine If circulating endogenous reproductive steroid levels were associated with the extent of coronary artery atherosclerosis. At necropsy, females which were pregnant one or more times were found to have coronary artery atherosclerosis which was one-fourth as extensive as that of intact females which had not been pregnant. Extent of coronary artery atherosclerosis correlated positively with mean total plasma cholesterol (Rho = 0.52, p<0.01) and Inversely with high density llpoproteln (HDL) cholesterol (Rho = − 0.48, p < 0.01) concentrations; both decreased during pregnancy. Additionally, the extent of coronary artery atherosclerosis was found to have a strong Inverse association (Rho = −0.66, p < 0.001) with an Index (area-under-the-curve) of magnitude and duration of the pregnancy-Induced elevation In plasma 17-B estradlol concentration. This association could not be explained by an Interrelationship between estradlol area-under-the-curve and either plasma total or HDL cholesterol concentrations. There was no relationship between atherosclerosis extent and a similar Index of plasma progesterone concentrations. These findings provide evidence for an Inhibitory effect of endogenous estrogen on the progression of coronary artery atherosclerosis.

Effect of obesity and fertility status on sex steroid levels in men

Endocrine studies were performed on fertile and infertile obese men and compared with fertile and infertile nonobese men in order to determine the independent and codependent effects of obesity and fertility status on the male hypothalamic-pituitary gonadal axis. The obese infertile group exhibited significant endocrinologic changes as compared with fertile nonobese control group which was not observed in any of the other three groups. Serum testosterone was significantly lower. The testosterone/estradiol ratio was significantly lower despite a lack of significant change in serum estradiol levels. Serum steroid hormone binding globulin (SHBG) was significantly lower which correlated with elevated bioavailability of both testosterone and estradiol in the obese infertile group. Serum luteinizing hormone levels were no different, suggesting that free testosterone levels were unchanged. Obese infertile men exhibit endocrinologic changes that are not observed in men with either obesity or infertility alone. Reduction of serum SHBG, total testosterone, and testosterone/estradiol ratio appear to be a marker of infertility among obese men.

Anabolic steroids and aggressive behavior in cynomolgus monkeys

An animal model was employed to examine the effect of testosterone on aggressive behavior patterns. Ten cynomolgus monkeys were assigned to either an experimental or a control group and given biweekly injections; the experimental group received testosterone propionate, and the controls a sham solution. Prior to and upon the completion of an 8-week treatment period, behavioral observations were conducted. Although the administration of testosterone resulted in a significant increase in aggression, more important was the finding that changes in behavior were mediated by social status; that is, the incidence of both contact and noncontact aggression in dominant monkeys was far greater than the frequency of these behaviors in subordinate monkeys. These data are discussed in terms of the potential role of anabolic steroids as a risk factor in cardiovascular disease.

Acute Stress Reactivity from Contested Dominance in Dominant and Submissive Males

We examined the cardiovascular and testosterone responses of dominant and submissive males to an interpersonal challenge of dominance status. Twenty college-aged students rated their dominance to predefined reference groups and engaged in a debate against a trained technician. Throughout the task, they were continuously given false feedback regarding biochemical substances in the plasma that purportedly covaried with dominance. Covariance analyses revealed that the task created greater heart rate reactivity and lower testosterone levels on the part of submissive subjects when contrasted with those scoring high in self-reported dominance. Interpretation of these data emphasizes the importance of an interactionist perspective in research dealing with acute stress reactivity.

Nonhuman Primate Models of Atherosclerosis: Potential for the Study of Diabetes Mellitus and Hyperinsulinemia

Nonhuman primates have been used for many years to investigate the pathogenesis and progression of atherosclerosis. The use of these animal models has resulted in a better understanding of the risk factors associated with atherosclerosis. Nonhuman primates that have consumed an atherogenic diet for several years develop lesions that are comparable to those found in human beings. Diabetes, both spontaneous and chemically induced, has been described in a number of nonhuman primate species. These diabetic models may be used to understand the accelerated progression and vascular complications of atherosclerosis in diabetic human beings.

Hormonal determinants of apolipoprotein B,E receptor expression in human liver. Positive association of receptor expression with plasma estrone concentration in middle-aged/elderly women

The relationships of the expression of hepatic low-density lipoprotein (LDL) receptors (apo B,E receptors) to several plasma hormone concentrations were examined in 15 fasted women aged 37-75 years (mean, 57 years), who were undergoing laparotomy for non-neoplastic disease. No subject had clinical or biochemical evidence of familial hypercholesterolemia, renal disease, hepatic disease, or endocrine disease. Hepatic apo B,E receptor expression was quantified in vitro as the EDTA-suppressible binding of 125I-labeled human LDL (15 micrograms protein/ml) by liver homogenate at 37 degrees C; values were 23-75 ng LDL protein/mg cell protein (mean, 47 ng/mg). Receptor expression was strongly correlated with plasma estrone concentration (rs = +0.70, P = 0.035), but was unrelated to the concentrations of testosterone, thyroxine, free triiodothyronine, cortisol, sex hormone-binding globulin (SHBG) or cortisol-binding globulin. Insulin and estradiol concentrations were mostly very low. The correlation of receptor expression with plasma total estrone concentration reflected associations with both the albumin-bound (rs = +0.78, P = 0.014) and unbound (rs = +0.80, P = 0.009) fractions, but not with the SHBG-bound fraction (rs = -0.22, P = 0.574), of this hormone. As the non-SHBG-bound fractions of gonadal steroids are considered to be the biologically active components, these results are consistent with experimental evidence that the synthesis of apo B,E receptors in hepatocytes is stimulated by estrogens, and suggest that circulating estrone may be the major hormonal determinant of receptor expression in fasted middle-aged/elderly women.

Oral contraceptive administration, interfemale relationships, and sexual behavior in Macaca fascicularis

The effects of oral contraceptive administration on the social relationships of adult female cynomolgus monkeys (Macaca fascicularis) were examined. Ten females were administered ethinyl estradiol/ethynodiol diacetate (Demulen), 10 were administered ethinyl estradiol/norgestrel (Ovral), and 10 served as a control group. The monkeys lived in social groups of 5 females each, and patterns of social interaction and social status were recorded. Interfemale relationships were also observed when a vasectomized male was placed in each social group for 50 min, once/week. During the latter observations, preliminary data on the effects of oral contraceptive treatment on sexual interaction were also collected. In the absence of the male, interfemale agonistic interactions and time spent alone were influenced by social status but not by oral contraceptive treatment. Time spent in passive body contact, an affiliative state, was reduced by Ovral treatment. In the presence of the male, dominant females aggressively interfered with the sexual interactions of subordinates. This aggression resulted in the termination of a greater proportion of the sexual interactions of subordinates than dominants in the control group only, indicating suppression of this type of interaction by oral contraceptive treatment. Other effects included a decreased frequency of ejaculation with Ovral-treated females. These results suggest that oral contraceptives may suppress certain types of female agonistic behavior (e.g., in the context of mate competition) and some oral contraceptives may interfere with sexual activity. More broadly, these findings indicate that intrasexual competition for access to mates may occur in females as well as males.