K. D. Carey

Estradiol-17 beta affects estrogen receptor distribution and elevates progesterone receptor content in baboon aorta.

We used the synthetic estrogen R2858 (moxestrol) and estradiol-170, respectively, to characterize the estrogen receptor in baboon (Papio sp.) aortic or myocardial cytoplasmic and nuclear preparations. We observed regional differences in the cytoplasmic fraction estrogen and progesterone receptor content of aortic arch, thoracic aorta, and abdominal aorta when tissues from either oophorectomized or oophorectomized estradiol-170-treated subjects were compared. The estrogen receptor content was highest in the abdominal aorta and lowest in the aortic arch. In contrast, the cytoplasmic fraction progesterone receptor content was highest in the aortic arch and lowest in the abdominal aorta. The nuclear fraction estrogen receptor could not be demonstrated in preparations from cardiovasculature of oophorectomized female baboons. The use of Silastic implants to administer a physiologic concentration of estradiol-170 to oophorectomized female baboons caused a 20% to 50% reduction in cytoplasmic fraction estrogen receptor content, which was quantitatively accounted for by the appearance of estrogen receptor in the corresponding nuclear aortic or myocardial preparation. Estrogen administration caused a 20% to 40% increase inc cytoplasmic fraction progesterone receptor content in both myocardium and aorta; however, differences were significant only for abdominal aorta (p < 0.05). Estradiol- 170 treatment caused a tenfold increase in uterine cytoplasmic fraction progesterone receptor content in treated as compared to oophorectomized control females, suggesting that baboon cardiovasculature is less sensitive to changes in endogenousestrogen concentration than is uterus. The ability of estradiol-170 to affect apparent intracellular distribution of baboon cardiovascular estrogen receptors and to elevate cytoplasmic fraction progesterone receptor content suggests that these estrogen receptors are physiologically functional and indicates that estrogen may directly regulate primate cardiovascular cell function.

Deferred effects of preweaning diet on atherosclerosis in adolescent baboons.

We examined the effects of breast and formula feeding during infancy on the serum llpoprotelns and on atherosclerosis in young adult baboons. Baboons were breastfed (n = 13) or formula-fed (n = 32) until weaning at 16 weeks of age and thereafter they were fed a diet containing 1.7 mg cholesterol/kcal and 40% of calories as lard until 5 years of age. At 12 weeks of age, breast-fed baboons had higher serum high density lipoproteln cholesterol concentration (HDL-C, 68 vs. 51 mg/dl), lower serum trlglycer- Ide concentration (37 vs. 68 mg/dl), and lower very low density plus low density lipoproteln cholesterol (VLDL + LDL-C) to HDL-C ratio (0.65 vs. 0.98) than formula-fed Infants. From weaning to 92 weeks of age, breast-fed baboons had a lower serum triglycerlde concentration (23 vs. 38 mg/dl) than formula-fed baboons. After weaning, the VLDL + LDL-C/HDL-C ratio Increased from 0.65 to 1.0 In breast-fed baboons, but decreased from 0.98 to 0.72 In formula-fed baboons. From 92 to 246 weeks of age, the VLDL + LDL-C/HDL-C ratio was consistently higher In breast-fed baboons compared to formula-fed baboons. At 5 years of age, baboons breast-fed as infants had a greater percentage of Intimal surface area Involved with atherosclerosis In the abdominal aorta, the lilac-femoral artery, the aortic arch, the brachial artery, and the carotid artery, than did those formula-fed as infants. The greater prevalence of lesions In breast-fed baboons was explained mainly by the higher VLDL + LDL-C/HDL-C ratio.

Two Major Loci Control Variation in β-Lipoprotein Cholesterol and Response to Dietary Fat and Cholesterol in Baboons

We explored the genetic control of cholesterolemic responses to dietary cholesterol and fat in 575 pedigreed baboons. We measured cholesterol in beta-lipoproteins (low density lipoprotein cholesterol [LDLC]) in blood drawn from baboons while they were consuming a baseline (low in cholesterol and fat) diet, a high-saturated fat (lard) diet, and a high-cholesterol, high-saturated fat diet. In addition to baseline levels (LDLC(Base)), we analyzed two variables for diet response: LDLC(RF), which represents the LDLC response to increasing dietary fat (ie, high-fat diet minus baseline), and LDLC(RC), which represents the LDLC response to increasing dietary cholesterol level (ie, high-cholesterol, high-fat diet minus high-fat diet). Heritabilities (h2) of the 3 traits were 0.59 for LDLC(Base), 0.14 for LDLC(RF), and 0.59 for LDLC(RC). In addition, LDLC(Base) and LDLC(RC) had a significant genetic correlation (ie, rhoG=0.54), suggesting that 1 or more genes exert pleiotropic effects on the 2 traits. Segregation analyses detected a single major locus that accounted for nearly all genetic variation in LDLC(RC) and some genetic variation in LDLC(Base) and LDLC(RF) and confirmed the presence of a different major locus that influences LDLC(Base) alone. Preliminary linkage analyses indicated that neither locus was linked to the LDL receptor gene, a likely candidate locus for LDLC. Detection of these major loci with large effects on the LDLC response to dietary cholesterol in a nonhuman primate offers hope of detecting and ultimately identifying similar loci that determine LDLC variation in human populations.

Cigarette smoking, dietary hyperlipidemia, and experimental atherosclerosis in the baboon.

In separate experiments, we fed 30 male and 25 female baboons a diet enriched in cholesterol and saturated fat for periods of 3.3 and 2.6 years. Using operant conditioning with water rewards, we trained the animals to puff on smoking machines in a human-like manner. Half of the animals smoked more than 40 cigarettes per day, while the remaining animals (controls) puffed air. Initially, the diet produced twofold (males) and threefold (females) elevations from baseline levels in serum cholesterol concentrations, but over the course of the experiments, the serum cholesterol decreased to 1.5 (males) and 2.0 (females) times baseline levels in both cigarette smokers and controls. Blood carbon monoxide concentration, plasma thiocyanate concentration, and urine cotinine concentration were significantly greater in smokers than in controls. Responses to smoking in males included lymphocytosis, elevated fasting blood glucose concentration, and decreased seminal vesicle weight. In females, hemoglobin and mean corpuscular hemoglobin concentrations were elevated. The extent of atherosclerosis was examined after 2.8 (males) and 1.6 (females) years of smoking. Among males, the extent of lesions in carotid arteries was significantly greater in smokers than in controls, but there were no significant differences in atherosclerosis in the aorta or the brachial, iliac-femoral, or coronary arteries. Among females, there were no significant differences in atherosclerosis between smokers and controls in any artery. These experiments show little effect of 2 to 3 years of cigarette smoke inhalation and concurrent modest elevation of blood carboxyhemoglobin on experimental atherosclerosis in the presence of moderate hyperlipidemia.

A major gene influences variation in large HDL particles and their response to diet in baboons

Some baboons accumulate appreciable amounts of large apoE-rich HDLs (HDL(1)) which are similar to those reported in humans with several different dyslipoproteinemias. We estimated HDL(1) cholesterol concentrations by gradient gel electrophoresis of serum samples obtained from 634 pedigreed baboons fed with three diets differing in levels of fat and cholesterol. The HDL(1) trait was highly heritable on each diet (0.390< or =h(2)< or =0.528). Segregation analyses yielded significant evidence that a single major gene plus polygenes affected HDL(1) on a high-fat low-cholesterol diet. The major gene explained approximately 56% of total trait variance and 90% of the additive genetic variance in HDL(1) levels in these baboons. Bivariate one-locus segregation analyses indicated that this major gene exerts significant pleiotropic effects on a number of traditional HDL traits on all three diets, including HDL size distributions, and concentrations of HDL-C, apoAI, and apoE. Linkage analyses showed that this major gene was not located in chromosomal regions that contain six candidate genes whose protein products are important to HDL metabolism (LCAT, CETP, APOA1, APOE, ABCA1, LIPC). Our results suggest this major gene in baboons plays a pivotal role in HDL metabolism, but is unlikely to code for any of the proteins previously implicated in studies of human HDL(1).

Genetic determination of HDL variation and response to diet in baboons

We fed 634 baboons three diets to assess the separate effects of increasing dietary fat and cholesterol intakes on three independent measures of HDL phenotype: concentrations of HDL cholesterol and apoAI, and size distributions of HDL cholesterol. Increasing dietary fat significantly increased concentrations of HDL cholesterol and apoAI (both, P<0.0001), but did not affect HDL particle sizes, whereas increasing dietary cholesterol increased HDL cholesterol (P<0.0001) concentrations and HDL particle sizes (P=0.08), but did not affect apoAI concentrations. A substantial proportion of variation in each of the HDL traits was influenced by genes (heritabilities ranged from 25 to 61%) and a common set of genes influenced HDL variation on each of the diets (genetic correlations ranged from 0.64 to 1.0). However, genes exerted a smaller effect on HDL response to changes of dietary fat and of dietary cholesterol. Therefore, dietary fat and cholesterol alter HDL levels and characteristics, but the dietary responses are not strongly mediated by additive genetic effects.

Gender and baboon aortic steroid hormone receptors.

To examine the potential of steroid hormones to serve as putative regulators of aortic cell function, we defined hormone receptor content and distribution In intact baboons. Total androgen receptor content In baboon aortic arch, thoracic arch, and abdominal aorta of young mature males was Indistinguishable from that of proestrus females. However, 30% to 40% of male aortic androgen receptors were In the nuclear fraction, whereas all aortic androgen receptors of proestrus females were In the cytoplasmlc fraction. Cytoplasmlc fraction estrogen receptor content of aortic arch and thoracic aorta of Intact males was indistinguishable from that of proestrus females. However, cytoplasmlc fraction estrogen receptor content of abdominal aorta of proestrus females was significantly greater than that of males. Nuclear fraction estrogen receptors were not detectable In either male or proestrus female baboon aortas. To assess effects of endogenous estrogen on aortic progesterone receptor content, we quantified cytoplasmlc fraction progesterone receptors and found that content of proestrus female aortic arch was not significantly different from that of males. However, cytoplasmlc fraction progesterone receptor content of thoracic and abdominal aorta of proestrus females was significantly higher than that of males. To determine whether differences In aortic receptor content or distribution were associated with changes In aortic cell function, we quantified the activity of two enzymes of glycosamlnoglycan metabolism. Aortic B-glucuronldase activity was not different In male or proestrus female baboons. Urldlne dlphosphate glucose (UDPG) dehydrogenase activity of aortic arch and thoracic aorta of proestrus female baboons was not different from that of males; however, UDPG dehydrogenase activity of abdominal aorta of proestrus females was greater than that of males. Our studies establish endogenous androgen regulation of Intracellular distribution of baboon aortic androgen receptors and imply that these receptors are physiologically functional. The higher cytoplasmlc fraction progesterone receptor content of female thoracic and abdominal aorta, as compared to that of males, suggests aortic estrogen receptors also are physiologically functional. These findings establish that baboon aortic steroid hormone receptor content and distribution Is sexually dimorphic, as Is the case for rodents. However, the essential Identity of B-glucuronldase or UDPG dehydrogenase activity In male and female baboon aortas Indicates that baboon aortic glycosamlnoglycan metabolism Is not sexually dimorphic. The fact that aspects of aortic steroid hormone receptor homeostasls and steroid hormone regulation of aortic UDPG dehydrogenase and B-glucuronldase activity significantly differ In baboons and rodents Implies complex effects of steroid hormones which may be speciesspecific.