Seasonal changes in haematology and metabolic resources in the tench

Significant variations in the number of white and red blood cells, haematocrit and haemoglobin were found throughout the year in sexually mature male and female tench Tinca tinca . In general, the lowest values were observed during autumn–winter and the highest during summer, with males exhibiting higher values than females. Plasma glucose, cholesterol and triglycerides were lower during the winter than during the summer–autumn seasons in both sexes. Gonado-somatic and hepato-somatic indices were inversely correlated in female tench throughout the year. Seasonal patterns in liver metabolic resources were very similar for both sexes. For males and females, liver glycogen and proteins increased during the autumn, whereas the liver stored lipid during spring. Dorsal muscle mainly deposited glycogen, whereas lipid was mainly stored in the ventral muscle. Relations between seasonal changes in environmental factors, such as feeding and temperature are discussed.     

Effects of long term low dose acrylamide exposure on rat bone marrow polychromatic erythrocytes

Abstract

I investigated whether long term low dose exposure to acrylamide increased micronucleus frequency in rat bone marrow polychromatic erythrocytes (PCEs). Twenty-five male and 25 female Wistar rats were used. Animals of each sex were segregated into two treatment groups and one control group. Each treatment group consisted of ten animals and each control group consisted of five animals. Acrylamide, 2 or 5 mg/kg/day, was administered to the treatment groups in their drinking water for 90 days. Twenty-four hours after the last treatment, bone marrow samples were obtained and analyzed for the frequency of micronucleated polychromatic erythrocytes (MNPCEs). The cytotoxic effect of acrylamide on bone marrow also was tested by assessing the polychromatic erythrocyte/normochromatic erythrocyte (PCE/NCE) ratio. Both doses of acrylamide significantly increased the frequency of MNPCEs in both male and female rats. Acrylamide also decreased the PCE/NCE ratio in both sexes compared to the control group. My study showed that chronic low dose exposure to acrylamide increased the formation of micronuclei in PCEs of male and female rat bone marrow.     

Age-related changes of lipid fractions and total fatty acids in the serum of female and male rats aged from 37 to 1200 days

1. Total lipids and the lipid fractions cholesterol ester, triacylglycerols, free cholesterol, free fatty acids and phospholipids as well as the fatty acid patterns of total lipids were measured in the serum of female and male rats (Wistar SPF, strain Hannover) aged 37-1213 days. 2. All parameters were monitored every 49th day. Five female and five male animals were used in each experiment. 3. All lipid fractions showed a significant positive linear regression vs age in both sexes. There were multiple significant differences in lipid fractions between the sexes. 4. Among the fatty acids only docosahexaenoic acid shows a significant correlation with age in both sexes.     

Sex differences in plasma cholesterol-esterifying activity in rats

Esterification of free cholesterol was investigated after incubation at 37 degrees C of plasma from immature and adult rats of both sexes kept on stock, fat-free, or cholesterol-supplemented diets. According to measurements of the decrease in free cholesterol, plasma from the fat-deficient rats showed the highest cholesterol-esterifying activity. Esterification was higher in the mature female rats than in the mature males on stock or cholesterol-containing diets, although no sex differences were observed in the sexually immature young or in the fat-free animals. There were no sex differences in the fatty acid composition of the plasma sterol esters, phospholipids, and triglycerides in the immature animals, but arachidonic acid increased at the expense of linoleic acid in the sterol ester fraction in the adult female (not, however, in the adult male). In the phospholipid fraction the higher ratio of palmitic to stearic acids in the male was confirmed. There was an increase in linoleic acid in all three plasma lipid fractions of the mature male after cholesterol feeding. It is suggested that cholesterol may inhibit the conversion of linoleate to arachidonate. During the incubation of plasma, there was little change in the distribution of fatty acids except for a decrease in palmitoleate, and increases in C(20) tri- and tetraenoic acids, in the sterol esters of mature female rats on the stock ration and the fat-free diet. These C(20) acids decreased concomitantly in the phospholipid fraction, as the transesterification reaction mechanism proposed by earlier workers would predict.     

Age-related changes of lipid fractions and total fatty acids in liver lipids and heart lipids of female and male rats aged 37-1200 days (liver) and 331-1200 days (heart)

1. Total lipids and the lipid fractions cholesterol ester, triacylglycerol, free cholesterol, free fatty acids and phospholipids, as well as the fatty acid patterns of total lipids, were measured in liver homogenates of female and male rats (Wistar SPF, strain Hannover) aged 37-1213 days. 2. The same parameters were measured in the apex of the heart in female and male rats aged 331-1213 days. 3. All parameters were monitored every 49th day. Five female and five male animals were used in each experiment. 4. The lipid fractions in liver showed a positive linear regression vs age, whereas all lipids in rat heart showed a negative regression vs age in both sexes. 5. The significance of regression vs age of fatty acids was much less than that in the lipid fractions of liver and heart of these animals.     

Age-related changes in haematology and serum chemistry of Weiser-Maples guineapigs (Cavia porcellus)

Age-related changes in haematology and serum chemistry values were examined in male and female Weiser-Maples guineapigs (Cavia porcellus). Haematological changes that significantly (P<0.01) correlated with ageing were increased white blood cell and neutrophil counts in both sexes, decreased lymphocyte counts in both sexes, decreased reticulocyte and platelet counts in males, and decreased basophil counts in females. For serum chemistry, increases in total protein, triglycerides, blood urea nitrogen and creatinine were seen in both sexes, along with increases in total cholesterol in males and sodium in females. Decreased alkaline phosphatase in both sexes and decreased chloride in males were significantly (P<0.01) associated with age. These age-related changes are compared with the published literature.     

Induced alteration of rat erythrocyte membrane with effect of pyrethroid based compounds

The effects of tetramethrin and prallethrin exposure on plasma total proteins, free amino acids, albumins, urea, urea nitrogen, uric acid, creatinine were tested. Serum SGOT, SGPT and lipid profile, antioxidants super oxide dismutase (SOD), catalase, GSH, G-Px, phospholipids, cholesterol, C/P ratio in membranes of erythrocyte and membrane fluidity were analyzed. The reason of the study were analyzed to examine the possessions of mosquito repellent pyrethroid (MRP) based compounds tetramethrin and prallethrin exposure on plasma profile, antioxidant status of erythrocyte membrane, membrane fluidity in male Wistar rats. We tested chronically for three months exposure every day (continuously for 8–10 h per day by inhalation) of tetramethrin and prallethrin markedly available (MRP) repellents treated on male Wistar rats. Our results confirmed that tetrarmethrin and prallethrin treatment effect of plasma profile alterations, and lipid homeostasis mechanism in Red Blood cells (RBCs). Tetramethrin and prallethrin treatment significantly increased in erythrocyte membrane phospholipids and decreased levels of cholesterol with no change of protein content, increased C/P ration levels. Inhalation of tetramethrin and prallethrin stimulate plasma biophysical and biochemical modify SGOT, SGPT, erythrocyte membrane cholesterol and phospholipid levels, individual phospholipids and membrane fluidity of exposure rats compared to controls.     

Reduction of hyperlipidemia in the LA/N-corpulent rat by dietary fish oil containing n-3 fatty acids

The LA/N rat, when homozygous for the corpulent gene (cp/cp), is obese, hyperphageous, hyperinsulinemic, hypertriglyceridemic and prone to the development of vascular and myocardial lesions. The hypertriglyceridemia, which in 3-month-old cp/cp males is 282 +/- 42 mg/dl and in females, 512 +/- 83 mg/dl, results from the presence of a large triacylglycerol-rich VLDL. The moderate hypercholesterolemia in these animals is largely due to markedly elevated HDL levels, which reach 172 +/- 21 mg total lipid/dl in males and 154 +/- 22 mg total lipid/dl in females. The LA/N-cp rat is thus an interesting animal model of endogenous hypertriglyceridemia in which to examine the hypolipidemic effects of pharmacological agents and also dietary oil supplements containing the n-3 fatty acids. In this study, 1-month-old male and female cp/cp rats were fed a normal low fat laboratory chow supplemented with either 10% olive oil or 10% redfish (Sebastes marinus) oil ad libitum for a period of 2 months. The redfish oil contained 4.9 +/- 0.1% of its total fatty acids as eicosapentaenoic (20:5(n-3)) and 2.3 +/- 0.5% as docosahexaenoic acid (22:6(n-3)), the predominant fatty acids being gondoic (20:1(n-3)), 21.9 +/- 0.9% and cetoleic acid (22:1(n-11)), 21.7 +/- 1.7%, which are of dietary origin. Daily caloric intake was similar to the oil-fed versus control rats. However, the oil-fed animals weighed significantly more than the controls after 2 months of oil supplementation. Redfish oil reduced serum triacylglycerols by 54% in males and 45% in females after 2 months. VLDL levels, after the same time period, were reduced by 44% in males and 39% in females. HDL lipid mass was significantly reduced in both sexes (by 27% in males and 49% in females). However, the levels remained above those of male LA/N +/+ rats of the same age and Long-Evens rats. Olive oil feeding significantly reduced serum cholesterol, triacyglycerols and phospholipids in male but only cholesterol and phospholipids in female animals. This oil had no significant effect upon VLDL total lipid levels in either sex, but significantly increased the particle diameter with a concomitant reduction in the cholesterol and phospholipid content. HDL total lipid levels were unaffected: However, HDL total cholesterol increased significantly in males only. Both oils markedly reduced serum LDL levels in both sexes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Two-week longitudinal survey of bone architecture alteration in the hindlimb-unloaded rat model of bone loss: sex differences

The goal of this study was to determine, through a longitudinal follow-up, whether sex influences bone adaptation during simulated weightlessness. Twelve-week-old male and female Wistar rats were hindlimb unweighted for 2 wk, and the time course of bone alteration was monitored in vivo by means of densitometry and unbiased three-dimensional quantitative microcomputed tomography at 7 and 14 days. Compared with male rats, female rats had twice more cancellous bone volume at the proximal tibia at baseline, and this bone volume continued to increase, whereas in males it stabilized. Conversely, cortical area was greater in males than in females, and in both sexes cortical bone was still expanding. Hindlimb unloading resulted in larger reductions in males than in females in both cortical and cancellous compartments. In females, trabecular thickness and number decreased mildly, whereas in males trabecular number was dramatically reduced. In both sexes, the trabecular network became less connected and more rod-like shaped. Bone cellular activities evaluated by histomorphometry showed decreased bone formation rate in both sexes and increased resorption activity only in males. In conclusion, in female rats unloaded-related cancellous alterations reversed the growing process, whereas in males, which show lower growth process, it induced an accentuation of age-related cancellous bone changes for most of the parameters.     

Stimulation of pituitary corticotrophs in the rat--ultrastructural studies

The ultrastructural changes occurring in the corticotrophs of adult male and female Sprague-Dawley rats at 2 and 6 weeks after bilateral adrenalectomy were assessed on both a qualitative and quantitative basis. Qualitative changes were similar to those previously described but at both time points, female rats showed more marked changes than males. Corticotroph hypertrophy reached a plateau in male animals between 2 and 6 weeks, but continued to increase in females. There was an increase in mean granule diameter in both sexes at 2 weeks after adrenalectomy. The changes induced by the daily administration of CRF for 2 weeks by intraperitoneal injection were also examined in male rats. CRF induced corticotroph hypertrophy at both 25 micrograms/Kg and 50 micrograms/Kg body weight and increased the granule content. The addition of vasopressin (VP) to the higher dose of CRF induced a further increase in cell area and reduction in granule content. Low dose CRF was associated with an increase in mean granule diameter, whereas a decrease was seen after high dose.     

Density-dependent sexual selection in external fertilizers: variances in male and female fertilization success along the continuum from sperm limitation to sexual conflict in the sea urchin Strongylocentrotus franciscanus

Sperm competition and female choice are fundamentally driven by gender differences in investment per offspring and are often manifested as differences in variance in reproductive success: males compete and have high variance; most females are mated and have low variance. In marine organisms that broadcast spawn, however, females may encounter either sperm limitation or sperm competition. I measured the fertilization success of male and female Strongylocentrotus franciscanus over a range of population densities using microsatellite markers. Female fertilization success first increased and then decreased with mate density, limited at low density by sperm limitation and at high density by polyspermy. Mate density affected variance in fertilization success in both males and females. In males, the variance in fertilization success increased with mate density. In females, the pattern was more complex. The variance in female success increased similarly to males with increased mate density but then decreased to low levels at intermediate densities, where almost all eggs were fertilized. As density increased further, the female variances again increased as polyspermy lowered average fertilization success. Male and female variances differed only at intermediate densities. At low densities, both sexes may be under selection to increase fertilization success; at intermediate densities, males may compete; and at high densities, both sexes may be under selection to increase success by increasing (males) or decreasing (females) likelihood of fertilization during sexual conflict. Only within a narrow range of densities do patterns of sexual selection mirror those typically noted in internally fertilizing taxa.     

Influence of gender on tamoxifen-induced biochemical changes in serum of rats

Tamoxifen, the widely prescribed drug in the prevention and therapy of breast cancer, may cause side effects which may be influenced by gender. The present study was undertaken to investigate the impact of gender on tamoxifen-induced toxic and biochemical changes following oral administration of tamoxifen at high dose level of 20 mg/kg once daily for a 2-week period in both male and female rats. The results showed marked increases in serum activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in female rats. In contrast, treatment with tamoxifen in male animals significantly decreased the activity of ALT, with a tendency for a decrease in serum AST levels. In female rats, a significant reduction in the serum activity of acid phosphatase (ACP) was noted, compared with a non-significant decrease in males. Non-significant changes in serum levels of alkaline phosphatase (ALP) were seen in both sexes. Tamoxifen lowered serum contents of total lipid and total cholesterol in both male and female rats. Serum levels of triglycerides were reduced in female rats as compared to a non-significant decrease in male animals. The serum albumin concentration was decreased in both male and female rats, while total protein was decreased only in female animals. Tamoxifen markedly increased serum levels of creatinine in female rats, compared with a non-significant rise in males. Total serum contents of calcium were similarly reduced in both males and females. This is the first study which points to gender-related differences in tamoxifen-induced toxic and metabolic changes in rats. The results indicated that females are more susceptible than males to tamoxifen toxicity, probably due to the ability of tamoxifen to antagonize the action of estrogen in females.     

Post-Mating Interactions and Their Effects on Fitness of Female and Male Echinothrips americanus (Thysanoptera: Thripidae), a New Insect Pest in China

Post-mating, sexual interactions of opposite sexes differ considerably in different organisms. Post-mating interactions such as re-mating behavior and male harassment can affect the fitness of both sexes. Echinothrips americanus is a new insect pest in Mainland China, and little is known about its post-mating interactions. In this study, we observed re-mating frequency and male harassment frequency and their effects on fitness parameters and offspring sex ratios of E. americanus females. Furthermore, we tested the impact of mating and post-mating interactions on fitness parameters of males. Our results revealed that the re-mating frequency in female adults was extremely low during a 30-day period. However, post-mating interactions between females and males, consisting mainly of male harassment and female resistance, did occur and significantly reduced female longevity and fecundity. Interestingly, increased access to males did not affect the ratio of female offspring. For males, mating dramatically reduced their longevity. However, post-mating interactions with females had no effects on the longevity of mated males. These results enrich our basic knowledge about female and male mating and post-mating behaviors in this species and provide important information about factors that may influence population regulation of this important pest species.     

Age-specific mating and reproductive senescence in the seven-spotted ladybird, Coccinella septempunctata

Abstract:  Adults of the seven-spotted ladybird, Coccinella septempunctata Linnaeus (Col., Coccinellidae) were paired for mating from very young to old age (1–50 days) to record the willingness to mate, attainment of sexual maturity and onset of reproductive senescence in both the sexes. Mating commenced after 4 and 2 days of emergence of male and female, respectively, and 100% mating was achieved at the young age in both cases (10 days). Willingness to mate decreased with increase in the age from 40 to 50 days of both the sexes. Ladybird exhibited protandry. Mating duration, fecundity and per cent viability of eggs of middle-aged males (20–30 days old) and females (20 days old) were the highest. Mating duration and per cent viability of eggs were male age dependent, whereas pre-oviposition and oviposition periods were mating stimulus dependent. Oviposition period and fecundity were female age-dependent responses. Fecundity was highest when 20-day-old female and 30-day-old male were paired. Onset of reproductive senescence started at the age of 30 days in males and 20 days in females. The present study confirms the effect of ageing on male and female C. septempunctata and supports the Hansen and Price [J. Evol. Biol. (1995) vol. 8, pp. 759–778] model that females mating with young and middle-aged males yield optimal quality progeny.     

Transient sex-related changes in the mice hypothalamo-pituitary-adrenal (HPA) axis during the acute phase of the inflammatory process

The potential role of endogenous sex hormones in regulating hypothalamo-pituitary-adrenal (HPA) axis function was investigated after a single injection of endotoxin in adult (8 week old) BALB/c mice of both sexes. The effect of LPS on plasma ACTH, corticosterone (B), testosterone and oestradiol (E) levels and on anterior pituitary (AP) ACTH and adrenal B contents at different times after treatment was studied. The results indicate that: (a) basal B but not ACTH plasma levels were significantly higher in female than in male mice; (b) LPS significantly increased both ACTH and B plasma levels over the baseline 2 h after injection, both hormone levels being higher in female than in male mice; (c) although plasma ACTH concentrations recovered the basal value at 72 h after LPS in animals of both sexes, plasma B levels returned to the baseline only at 120 h after treatment; (d) E plasma levels significantly increased 2 h after LPS and returned to the baseline at 72 h post-treatment, in both sexes; (e) at 2 h after LPS, testosterone plasma levels significantly decreased in male mice and increased in female mice, recovering the baseline level at 120 and 72 h after LPS, respectively; (f) AP ACTH content was similar in both sexes in basal condition and it was significantly diminished 72 h post-treatment without sex difference; whereas AP ACTH returned to basal content 120 h after LPS in males, it remained significantly decreased in females; (g) basal adrenal B content was higher in female than in male mice, and it significantly increased in both sexes 2 h post-LPS, maintaining this sex difference. Whereas adrenal B returned to basal content 72 h after treatment in male mice, it remained significantly enhanced up to 120 h post-LPS in female animals. The data demonstrate the existence of a clear sexual dimorphism in basal condition and during the acute phase response as well as in the recovery of the HPA axis function shortly after infection.     

Testosterone-dependent effects of galanin on pituitary luteinizing hormone secretion in male rats

Galanin is a 29-amino-acid peptide that colocalizes with GnRH in hypothalamic neurons. High concentrations of galanin are present in portal vessel blood of both male and female rats, and galanin receptors are present on gonadotropes in both sexes. Results from studies of female rats indicate that galanin acts at the level of the pituitary to directly stimulate LH secretion and also to enhance GnRH-stimulated LH secretion. The effects of galanin on pituitary LH secretion in male rats are relatively uncharacterized; thus, the present in vivo study was conducted 1). to examine the ability of galanin to affect basal or GnRH-stimulated LH secretion in male rats and 2). to determine whether the effects of galanin on LH secretion in male rats are testosterone-dependent. All three doses of galanin used (1, 5, and 10 micro g/pulse) significantly enhanced GnRH-stimulated LH secretion in intact male rats. Only the highest dose of galanin directly stimulated LH secretion (without GnRH coadministration) in intact males. Galanin did not directly stimulate LH secretion or enhance GnRH-stimulated LH secretion in castrated male rats. In fact, the highest dose of galanin inhibited GnRH-stimulated LH secretion in castrated males. Upon testosterone replacement, the ability of galanin to directly stimulate LH secretion and to enhance GnRH-stimulated LH secretion was restored in castrated males. These results suggest a role for galanin in the regulation of LH release in male rats and demonstrate that testosterone upregulates the ability of the pituitary to respond to the stimulatory effects of galanin.     

Male life history and the unusual adult sex ratios of redfronted lemur, Eulemur fulvus rufus, groups

In group-living species, theoretical considerations indicate the existence of a fundamental conflict of interest between the sexes over the adult sex ratio within groups. Females may derive certain benefits from living with many males. Males, in contrast, should generally try to monopolize access to a group of females. Which sex ultimately controls adult group sex ratio is poorly known. We examined this conflict between the sexes in redfronted lemurs, Malagasy primates characterized by an unusual lack of female-biased adult sex ratios. Using various demographic and behavioural data from several groups collected over 6 years, we examined (1) the proximate determinants of this unusual sex ratio, (2) the temporal distribution of female fertile phases within groups as a determinant of male monopolization potential, (3) sources of between-group variation in the adult sex ratio, and (4) possible social benefits of the relatively high number of males for both sexes. Birth and mortality rates were not sex biased and males migrated considerably more frequently than females, providing no proximate explanation for the unusual sex ratio. However, certain life history traits (fast maturation, short interbirth intervals) may ultimately play a role because they act to facilitate joint group transfers of male coalitions. Despite a relatively small female group size and an associated high monopolization potential, female oestrous synchrony may prevent the formation of single-male groups. Reduced male group size seems to be the main predictor of take-over rate, and, thus, infanticide risk, suggesting that both sexes may benefit from the high number of coresident males, thereby considerably defusing the conflict of interest between the sexes.     

Parallel evolutionary forces influence the evolution of male and female songs in a tropical songbird

Given the important role that animal vocalizations play in mate attraction and resource defence, acoustic signals are expected to play a significant role in speciation. Most studies, however, have focused on the acoustic traits of male animals living in the temperate zone. In contrast to temperate environments, in the tropics, it is commonplace for both sexes to produce complex acoustic signals. Therefore, tropical birds offer the opportunity to compare the sexes and provide a more comprehensive understanding of the evolution of animal signals. In this study, we quantified patterns of acoustic variation in Rufous‐and‐white Wrens (Thryophilus rufalbus) from five populations in Central America. We quantified similarities and differences between male and female songs by comparing the role that acoustic adaptation, cultural isolation and neutral genetic divergence have played in shaping acoustic divergence. We found that males and females showed considerable acoustic variation across populations, although females exhibited greater population divergence than males. Redundancy analysis and partial‐redundancy analysis revealed significant relationships between acoustic variation and ecological variables, genetic distance, and geographic distance. Both ambient background noise and geographic distance explained a high proportion of variance for both males and females, suggesting that both acoustic adaptation and cultural isolation influence song. Overall, our results indicate that parallel evolutionary forces act on male and female acoustic signals and highlight the important role that cultural drift and selection play in the evolution of both male and female songs.     

Age-related changes in enzyme activities, protein content and lipid composition of rat kidney brush-border membrane

Age-related changes in enzyme activities, protein electrophoretic patterns and lipid composition of kidney-brush-border membranes were studied in 10-20- and 30-month-old male and female Wistar rats. Polyacrylamide gel electrophoresis of membrane proteins revealed very little changes with increasing age, whether males or females were considered. The Km of three hydrolases - maltase, L-aminopeptidase and alkaline phosphatase - were not affected by age while the Vmax of maltase and alkaline phosphatase, but not of L-aminopeptidase, decreased from 10 to 30 months. The phospholipid to protein ratio which remained constant between 10 and 20 months, rose in both sexes from 20 to 30 months. In males, the cholesterol content of the membrane increased faster than that of phospholipid and the cholesterol over phospholipid ratio was then greater at 30 months than at 10 months, while in females this ratio remained unchanged in the course of aging. The fatty acid composition of the brush-border remained more or less constant with age in female rat whereas in the male, a 10% decrease in the proportion of arachidonic acid from 10 to 30 months was responsible for a lower unsaturation index.     

Thiazide-induced hypercholesterolemia: sex differences

Thiazide diuretics are used commonly to treat hypertension. Unfortunately, they also are known to elevate serum cholesterol levels. Because serum lipid fraction levels differ between the sexes, possible sex-related differences in thiazide-induced changes in serum total cholesterol (TC), triglycerides (TG) and high density lipoprotein cholesterol (HDL-C) levels were examined. Four groups of male and female hamsters were treated for a minimum of 3 months with hydrochlorothiazide (HCTZ) at zero, 1, 2 or 4 mg/kg/day. At zero dose, there was no difference in TG levels between the sexes; however, females had significantly higher TG concentrations than did males at 1, 2 and 4 mg HCTZ (all p less than 0.05). Females demonstrate a significant dose response with HCL-C levels increasing with increasing doses of HCTZ, (r = 0.983; p less than 0.02); in contrast males had a similar increase in HDL-C at all dose levels (all p less than 0.05) thus there was no demonstrable dose response (r = 0.539). Total cholesterol concentrations were significantly higher in the females than in males (p less than 0.05) at all 3 dose levels as well as at zero dose. Further, the females demonstrated a direct dose response in TC levels (r = 0.986; p less than 0.02) while the males showed no such dose response (r = 0.824; p less than 0.01). Based on these findings we conclude that: 1) HCTZ increases TG, TC and HDL-C levels in both male and female hamsters; 2) TC levels are higher in females than in males regardless of HCTZ dose; 3) only females show a dose-dependent increase in HCL-C and TC in response to HCTZ. These sex-related changes in lipid fractions occurring with HCTZ treatment, if they occur in humans, may contribute to sex-related differences in rates and severity of atherosclerosis in HCTZ-treated populations.