Pharmacokinetics of imipramine are affected by age and sex in rats

Chronic treatment with the antidepressant imipramine (IMI) leads to accumulation of imipramine's major metabolite desmethylimipramine (DMI) in the brain. Juvenile, young and middle-aged female rats, as well as juvenile and young male rats were treated chronically with imipramine (14 days) and analyzed 24 hours later for levels of IMI and DMI in the hypothalamus-preoptic area (HPA) and serum. Older animals of both sexes showed higher levels of DMI than juvenile animals, in both the HPA and serum. Females also had higher DMI levels than males at comparable ages. Analysis of IMI and DMI levels at intervals after a single imipramine injection suggested that the initial metabolism of imipramine is slower in older animals and in females (compared to males). The results indicate that age and gender alter the initial metabolism of imipramine, leading to enhanced accumulation of metabolites during chronic treatment in older animals and in female rats, compared to younger rats and males, respectively.     

Testosterone and imipramine have antidepressant effects in socially isolated male but not female rats

RationaleAffective disorders are twice as likely to occur in women as they are in men suggesting a critical role for gonadal hormones in their etiology. In particular, testosterone has been shown to have protective effects in men.ObjectiveTo investigate antidepressant effects and interactions between testosterone and imipramine in socially isolated male and female rats.MethodsA chronic social isolation model was used to induce an anxiety and depressive-like state in adult gonadectomized (Gnx) male and ovariectomized (Ovx) female rats receiving chronic testosterone and imipramine treatments. Their anxiety and depression-like behaviors were examined using the light–dark box, elevated plus maze, open field, sucrose preference and novelty induced hypophagia tests.ResultsIn socially isolated rats, the anxiolytic and antidepressant effects of testosterone and imipramine were limited to male rats. Additionally, testosterone enhanced the neurogenic effect of imipramine on hippocampal cell proliferation in male rats. Although female rats exhibited signs of anxiety and depressive-like behaviors following social isolation, testosterone and/or imipramine administration had no anxiolytic or antidepressant effects in Ovx females.ConclusionsTestosterone and imipramine had anxiolytic and antidepressant effects in socially isolated male, but not female rats. Testosterone enhanced the effect of imipramine on cell proliferation in the hippocampus of male rats.     

Chronopharmacokinetics of Imipramine and Desipramine in Rat Forebrain and Plasma After Single and Chronic Treatment with Imipramine

Daily variations in the pharmacokinetics of imipramine (IMI) could contribute to circadian phase-dependent effects of the drug. Therefore, the chronopharmacokinetics of IMI and its metabolite, desipramine (DMI), were studied after single and chronic application. Male rats were synchronized to a 12:12 hour lightdark (L:D) regimen with lights on from 07:00 to 19:00 (dark, 19:00-07:00). In single-dose experiments rats were injected with IMI (10 mg/kg) i.p. or i.v. at 07:30 or 19:30 and groups of rats were killed 0-22 hours thereafter. After chronic application of IMI in drinking water (≈ 15 mg/kg/d) groups of rats were killed during the 14th day of treatment at 02:00, 08:00, 14:00, and 20:00, respectively. Brain and plasma concentrations of IMI and DMI were determined by reversed-phase high-performance liquid chromatography with ultraviolet detection. After single i.p. application of IMI, maximal brain concentrations (C_max) of IMI and DMI were nearly twofold higher in darkness (IMI, 4.8 μg/g; DMI, 1.8 μg/g) than in light (IMI, 2.85 Mg/g; DMI, 0.85 Mg/g). Also, the area under the curve (AUC) (0-22 hours) was about 1.6-fold greater in darkness than in light for IMI and DMI; half-lives were not circadian phase dependent. After i.v. injection of IMI, the AUC in brain was also about 30% greater in darkness than in light. After chronic application of IMI in drinking water, brain concentrations of IMI and DMI varied more than threefold within 24 hours. The data demonstrate that the pharmacokinetics of IMI and DMI are circadian phase dependent. It is assumed that circadian variations in drug distribution are more likely to contribute to the drug's chronopharmacokinetics than variations in the drug's metabolism. The 24-hour variations in the drug's concentrations after chronic IMI application in drinking water can be explained by the drinking behavior of the rats, which by itself is altered by IMI.     

Comparison of plasma corticosterone- and progesterone-binding activity in rat and human

Corticosterone-and progesterone-binding activity were measured by saturation analysis, with dextran-charcoal separation, in plasma obtained from male and female rats, and a normal male and female human. In plasma from normal male and female rats, progesterone was much less effective than corticosterone in displacing ³H-corticosterone from plasma protein binding sites although the parallelism of the displacement curves indicated competition for the same binding sites. In plasma from the normal male human, corticosterone and progesterone were equally effective in displacing ³H-corticosterone. However, ³H-progesterone showed no apparent binding to either rat or human plasma proteins, suggesting that dextran-charcoal effectively removed progesterone from transcortin binding sites at 4°C. This observation was confirmed by multiple equilibrium dialysis. In dialysis, ³H-corticosterone and ³H₃-progesterone were bound equally by human plasma, but rat plasma bound ³H-corticosterone to a much greater extent than it did ³H-progesterone. These data indicate that, in contrast to human plasma, rat plasma has much greater affinity for corticosterone than for progesterone.     

Sex differences in oxidative stress induced by benzene in rats

Role of sex differences on oxidative stress induced by benzene has been studied in liver, kidney and lungs of rat. It was observed that benzene administration enhanced lipid peroxidation in liver, kidney and lungs of rat, nevertheless, significant variations were recorded in male and female rats. Decrease of GSH and CYTP(450)2E1 was higher in female rats than male rats except lungs. The results suggest that oxidative stress induced by benzene is higher in female rats.     

Sex differences in the lung ACE/ACE2 balance in hypertensive rats

The angiotensin-converting enzyme (ACE)/Angiotensin II (Ang II) and angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7) (Ang-(1-7)) pathways are coexpressed in most tissues. The balance between these pathways determines, at least in part, whether tissue damage will occur in response to pathological stimuli. The present study tested the hypothesis that male sex and high blood pressure are associated with ACE/ACE2 imbalance in the lungs. Experiments were conducted in male and female Wistar rats and spontaneously hypertensive rats (SHRs). Lung ACE and ACE2 gene expression was also evaluated in normotensive and hypertensive humans using the Genotype-Tissue Expression (GTEx) project. Compared with Wistar rats and female SHRs, male SHRs displayed reduced lung ACE2 mRNA, ACE2 protein abundance and ACE2 activity, and increased Ang II concentration. Lung ACE mRNA levels were higher in male SHRs than in Wistar rats, whereas lung ACE protein abundance and activity were similar among the four groups of rats. Lung Ang-(1-7) concentration was higher in female than in male SHRs (89 ± 17 vs. 43 ± 2 pg/g, P<0.05). Lung ACE to ACE2 mRNA expression in hypertensive patients was significantly higher than that in normotensive subjects. Taken together, these results demonstrate that male hypertensive rats display imbalance between the ACE/Ang II and ACE2/Ang-(1-7) pathways in the lungs mainly attributable to ACE2 down-regulation. Further studies should be conducted to investigate whether this imbalance between ACE/ACE2 may promote and accelerate lung injury in respiratory infections, including coronavirus disease 2019 (COVID-19).     

The metabolism of progesterone by animal tissues in vitro. Sex and species differences in conjugate formation during the metabolism of [4-14C]progesterone by liver homogenates

1. Sex and species differences during the metabolism of [4-¹⁴C]progesterone by liver homogenates from rat, rabbit, guinea pig and hamster have been investigated. 2. Liver homogenate from male rat formed `water-soluble' metabolites faster and in significantly larger amounts than did liver homogenate from female rat. About 65–70% of the added progesterone was conjugated as glucuronide by liver homogenate from male rat and about 45–50% by that from female rat. Liver homogenate from male rat also formed glucuronides faster than did liver homogenate from female rat. Sulphate formation was low (8–16%) in liver homogenates from both male and female rats. 3. Hamster-liver homogenate did not show any sex difference in the rate of formation of `water-soluble' metabolites, but a sex difference was observed in the amount of free steroids recovered at low tissue:steroid ratios. Liver homogenate from female hamster formed glucuronides faster and in significantly larger amounts than did liver homogenate from male hamster, the reverse of what was found in rat liver. 4. Liver homogenates from male and female rabbits and guinea pigs formed `water-soluble' metabolites that were almost entirely glucuronides. 5. Neither rabbit liver nor guinea-pig liver showed any significant sex difference in the rate or amount of formation of total `water-soluble' metabolites or glucuronides, but guinea-pig liver was considerably less active than rabbit liver. 6. Glucuronides were quantitatively the major type of conjugate formed by the liver homogenates from both sexes of all species except the male hamster.     

Gender difference in BK channel expression in amygdala complex of rat brain

The expression of large-conductance Ca²⁺-activated K⁺ (BK) channel protein in amygdala complex was higher in adult (8-10 weeks old) male rats than in female. Castration at 4-6 weeks old significantly reduced BK channel expression in amygdala to the level similar to that in female. Immunocytochemical analyses of pyramidal-like neurons isolated from amygdala revealed that somas with relatively large size were highly immunoreactive to both anti-androgen receptor (AR) and anti-BK channel antibodies, while those with smaller size were not. The double-immunopositive neurons were dominant (60%) among pyramidal-like neurons isolated from amygdala of male rats but rare among those from female. The membrane current sensitive to penitrem A, a BK channel blocker, was the major K⁺ current component in large neurons and showed higher current-density than that in smaller ones. These results suggest the gender-dependent cell population expressing BK channels in amygdala complex and its up-regulation by AR stimulation.     

Effects of Female Hormones (17β-Estradiol and Progesterone) on Nitric Oxide Production by Alveolar Macrophages in Rats

The effect of female sex hormones on nitric oxide (NO) production was studied in alveolar macrophages (AMs). Male rats were treated with endotoxin (LPS) intratracheally or saline as control. AMs were obtained by bronchoalveolar lavage 90 min later and were cultured in the presence or in the absence of LPS and 17β-estradiol or progesterone (10⁻⁹to 10⁻⁴M). NO production was assessed by measurement of nitrites in the medium. In some experiments, NO production by AMs was measured in intratracheally LPS-treated orchidectomized rats or in female control and ovariectomized rats. Both spontaneous and stimulated NO production were higher in AMs from female than from male rats, but without statistical significance. However, ovariectomy induced significant inhibition in spontaneous production of NO by AMs. In orchidectomized rats, the NO response by AMs to LPS stimulation relative to spontaneous NO production was significantly downregulated. Female sex hormones in physiological concentrations seem to be necessary for spontaneous NO production in female rats. Pharmacological doses of estradiol inhibitedin vitroLPS-stimulated NO production in AMs of both saline- and LPS-treated rats, and basal NO production only in LPS-treated male rats. Progesterone at 10⁻⁴M inhibited basal andin vitroLPS-stimulated NO generation by AMs of both saline- and LPS-treated male rats. In LPS-treated female ratsin vitroLPS-stimulated NO production was not affected by estradiol treatment. In ovariectomized LPS-treated female rats progesterone at 10⁻⁵M significantly inhibited NO production byin vitro-stimulated AMs. Thus female sex hormones may contribute to the gender-related differences in the immune response.     

Chronopharmacokinetics of imipramine and desipramine in rat forebrain and plasma after single and chronic treatment with imipramine.

Daily variations in the pharmacokinetics of imipramine (IMI) could contribute to circadian phase-dependent effects of the drug. Therefore, the chronopharmacokinetics of IMI and its metabolite, desipramine (DMI), were studied after single and chronic application. Male rats were synchronized to a 12:12 hour light:dark (L:D) regimen with lights on from 07:00 to 19:00 (dark, 19:00-07:00). In single-dose experiments rats were injected with IMI (10 mg/kg) i.p. or i.v. at 07:30 or 19:30 and groups of rats were killed 0-22 hours thereafter. After chronic application of IMI in drinking water (approximately 15 mg/kg/d) groups of rats were killed during the 14th day of treatment at 02:00, 08:00, 14:00, and 20:00, respectively. Brain and plasma concentrations of IMI and DMI were determined by reversed-phase high-performance liquid chromatography with ultraviolet detection. After single i.p. application of IMI, maximal brain concentrations (Cmax) of IMI and DMI were nearly twofold higher in darkness (IMI, 4.8 micrograms/g; DMI, 1.8 micrograms/g) than in light (IMI, 2.85 micrograms/g; DMI, 0.85 microgram/g). Also, the area under the curve (AUC) (0-22 hours) was about 1.6-fold greater in darkness than in light for IMI and DMI; half-lives were not circadian phase dependent. After i.v. injection of IMI, the AUC in brain was also about 30% greater in darkness than in light. After chronic application of IMI in drinking water, brain concentrations of IMI and DMI varied more than threefold within 24 hours. The data demonstrate that the pharmacokinetics of IMI and DMI are circadian phase dependent. It is assumed that circadian variations in drug distribution are more likely to contribute to the drug's chronopharmacokinetics than variations in the drug's metabolism. The 24-hour variations in the drug's concentrations after chronic IMI application in drinking water can be explained by the drinking behavior of the rats, which by itself is altered by IMI.     

Desmethylimipramine Enhances the Release of Endogenous GABA and Other Neuro trans mitter Amino Acids from the Rat Thalamus

The influence of desmethylimipramine (DMI) on the release of endogenous gamma-aminobutyric acid (GABA) and some other amino acids from the rat thalamus was studied with a push-pull perfusion technique. Following HPLC the amino acids were fluorimetrically estimated. Added to the perfusion medium at a concentration of 10 mumol L-1, DMI caused a 5- to 10-fold increase in the release of GABA. Similar effects were found with imipramine, trimeprimine, haloperidol, and propranolol. The elevation of GABA release induced by DMI was Ca dependent. The release of aspartate and glutamate was also increased by DMI, but in contrast to K ions, DMI did not reduce the thalamic output of glutamine.     

The effect of sex on the uptake of very low density lipoprotein triglyceride fatty acid from the plasma of the rat in vivo.

Radioactive very low density lipoprotein (VLDL) was prepared by perfusion in vitro of livers isolated from normal fed male and female rats with [1-¹⁴C] oleate or [9, 10-³H] oleate, respectively. These VLDL, whose properties differed due to sex, were mixed. Aliquots of the mixture were injected intravenously into fasted male and female rats and the decay of the radioactivity (¹⁴C and ³H) was measured. Disappearance of radioactivity from plasma triglyceride was more rapid in female animals. Plasma half-life of ¹⁴C and ³H was 42.5±3.7 and 49.7±4.4 minutes, respectively, when the VLDL mixture was injected into male rats. The corresponding values in female rats were 28.3±1.1 and 30.7±1.7, respectively. These data suggest strongly that the rate of utilization of VLDL triglyceride fatty acid is more rapid in the female than in the male, and that the properties of the VLDL particles are of less importance than innate sex differences in the recipient for the rate of clearance of triglyceride fatty acids.     

Opposite effects of acute and repeated administration of desmethylimipramine on adrenergic responsiveness in rat pineal gland.

The effect of acute and repeated desmethylimipramine (DMI) treatment on catecholamine-stimulated production of adenosine 3', 5'-monophosphate (cyclic AMP) in rat pineal gland was studied $\text{in}$$\text{vivo}$. In rats exposed to continuous illumination, the administration of isoproterenol (2μmol/kg) to control animals produced a marked increase in the concentration of cyclic AMP in pineal gland. In contrast, norepinephrine (2μmol/kg) failed to increase the levels of cyclic AMP. After acute treatment with DMI (single injection, 38μmol/kg, i. p.), the isoproterenol-induced rise in cyclic AMP was not significantly different from that measured in control animals. However, acute DMI treatment did allow a significant elevation in the concentration of cyclic AMP in pineal gland in response to norepinephrine. In rats given nine injections of DMI (38μmol/kg, i.p., twice daily) neither isoproterenol nor norepinephrine caused a significant increase in the concentration of cyclic AMP in pineal glands. Although acute treatment with DMI had no significant effect on [³H] dihydroalprenolol binding, chronic treatment with DMI significantly reduced [³H] dihydroalprenolol binding in the pineal gland. The results of this study suggest that while a single administration of DMI can enhance adrenergic responses elicited by norepinephrine, chronic administration of DMI leads to compensatory decreases in receptor density and adrenergic responsiveness.     

Possible relationship of the hepatic microsomal ATP-dependent calcium pump to sex differences in triacylglycerol synthesis

Microsomes were isolated from livers of fed male and female rats and the rates of incorporation of sn-[¹⁴C]-glycerol-3-phosphate into phosphatidate, diacylglycerol and triacylglycerol by the microsomes were measured. Simultaneously, microsomal ATP-dependent uptake of calcium was evaluated and correlated with synthesis of phosphatidate from sn-glycerol-3-phosphate. The rate of glycerolipid synthesis by hepatic microsomes from female rats was greater than that of microsomes from male rats. By contrast, the active accumulation of calcium and subsequent inhibition of synthesis of phosphatidate from glycerol-3-phosphate was lower in microsomes from livers of female rats than from male animals. This reciprocal relationship between uptake of calcium and incorporation of sn-glycerol-3-phosphate into phosphatidate as reported earlier (Biochem. Biophys. Res. Commun. $\text{78}$, 1053–1059 (1977)) may, in part, be responsible for the differences in the rates of hepatic triacylglycerol synthesis between livers from male and female rats.     

Organ specificity of the sex dependent regulation of aryl hydrocarbon hydroxylase (AHH) in rat

Aryl hydrocarbon hydroxylase (AHH) activity was measured in liver, kidneys and lungs of control and gonadectomized Sprague-Dawley rats. There was a six-fold difference in hepatic AHH activity between male and female rat. Activity in male was highest, castration reduced this activity by about 50%, whereas ovariectomy had little effect on activity in female. No sex difference in lung AHH activity was discernable; on the other hand kidney AHH activity was higher in females than in males. These data suggest that, at least in the rat, sex dependent regulation of microsomal mixed function oxygenases is organ specific.     

Sex-dependence of the metabolism of aldosterone in adrenalectomized and intact rats

The metabolism of aldosterone at physiological levels was shown to be significantly different in male and female rats: more aldosterone was metabolized in the male rats leading to significantly higher quantities of non-extractable polar derivatives of aldosterone in all subcellular fractions of kidney, particularly in the cytosol fractions. These results may be correlated with our findings in which it was shown that the physiological responses to aldosterone in both adrenalectomized and intact rats were significantly greater in the males than the females. These sex differences support the concept that the metabolism of aidosterone may be essential for the components of the physiological response to aldosterone to occur. Furthermore, the sex-dependence of the metabolism of aldosterone appears to be independent of the presence of the previously identified protein receptor-hormone complexes. At all dosages within the physiological range, no significant differences were observed between the extent of the ³H-aldosterone labeling of these binding proteins in the kidney cytosol fractions of male and female adrenalectomized rats, even at dosages where no physiological response was demonstrable in the females.     

Male-Specific Differences in Proliferation,Neurogenesis, and Sensitivity to Oxidative Stress in Neural Progenitor Cells Derived from a Rat Model of ALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive motor dysfunction and the loss of large motor neurons in the spinal cord and brain stem. A clear genetic link to point mutations in the superoxide dismutase 1 (SOD1) gene has been shown in a small group of familial ALS patients. The exact etiology of ALS is still uncertain, but males have consistently been shown to be at a higher risk for the disease than females. Here we present male-specific effects of the mutant SOD1 transgene on proliferation, neurogenesis, and sensitivity to oxidative stress in rat neural progenitor cells (rNPCs). E14 pups were bred using SOD1^G93A transgenic male rats and wild-type female rats. The spinal cord and cortex tissues were collected, genotyped by PCR using primers for the SOD1^G93A transgene or the male-specific Sry gene, and cultured as neurospheres. The number of dividing cells was higher in male rNPCs compared to female rNPCs. However, SOD1^G93A over-expression significantly reduced cell proliferation in male cells but not female cells. Similarly, male rNPCs produced more neurons compared to female rNPCs, but SOD1^G93A over-expression significantly reduced the number of neurons produced in male cells. Finally we asked whether sex and SOD1^G93A transgenes affected sensitivity to oxidative stress. There was no sex-based difference in cell viability after treatment with hydrogen peroxide or 3-morpholinosydnonimine, a free radical-generating agent. However, increased cytotoxicity by SOD1^G93A over-expression occurred, especially in male rNPCs. These results provide essential information on how the mutant SOD1 gene and sexual dimorphism are involved in ALS disease progression.     

Production of anisogametes and gamete motility dimorphism in Monostroma angicava

 The reproductive strategy of a marine alga with a heteromorphic biphasic life cycle was studied by analyzing various sexual reproductive characters in light of the evolution of anisogamy. Gametophytes of Monostroma angicava were dioecious and their gametes were slightly anisogamous. Volume of gametangium, density of gametangia and area of mature gametangial parts on each gametophyte did not differ from male to female. Therefore, the reproductive biomass investment for gamete production was considered to be the same for each sex. Anisogamy in this alga appeared to be derived from the difference in the number of cell divisions during gametogenesis, because the majority of male gametangia each produced 64 (2⁶) gametes and the female produced 32 (2⁵) gametes. This corresponded with measurements of cell size in male and female gametes. Further, the sex ratio was 1:1 for sexually mature plants sampled at Charatsunai. Therefore, it was suggested that in the field twice as many male gametes are released as female gametes. Liberated gametes of both sexes showed positive phototaxis. The swimming velocity of freshly liberated male gametes was a little higher than that of female gametes. Male gametes had the potential to swim for ca. 72 h and female gametes for ca. 84 h. The difference in gamete motility between the two sexes seemed to be related to cell size. Planozygotes were negatively phototactic and swam more rapidly than gametes of either sex. Received: 5 March 1997 / Revision accepted: 18 July 1997     

Essential trace metals and specific organ weights in diet-restricted and ad lib-fed rats

Wistar male rats were exposed to nickel oxide (NiO) aerosols (mass median aerodynamic diameter, 1.2 μm). The average exposure concentration was controlled from low level (0.6 mg/m³) to high level (8.0 mg/m³) and total exposure time ranged from 140 to 216 h. Some rats were sacrificed just after the exposure, whereas others were exposed for 1 mo and kept for a 1-yr clearance period before sacrifice. There were no differences in body weight gain between NiO exposure groups and controls. Nickel concentrations in lungs of exposure groups were much higher than those of controls. No apparent deposition of nickel was observed in liver, kidney, spleen, heart, brain, and blood, but lung burdens of up to about 2.35 mg of NiO were found. The apparent deposition fractions were 19.8 and 14.5% after the exposure to average concentrations of 1.4 and 6.5–7.0 mg/m³, respectively. The clearance rate of NiO deposited in lungs may be small.     

Assessment of rat brain alpha1-adrenoceptor binding and activation of inositol phospholipid turnover following chronic imipramine treatment

Chronic (21 days) treatment of rats with imipramine (10 mg/kg) did not change the density or affinity of alpha₁-adrenoceptors as measured by the specific binding of [³H]prazosin in rat cortical membranes, but produced the expected significant decrease in the density of beta-adrenoceptors labeled by [¹²⁵I]iodocyanopindolol. The functional status of brain alpha₁-adrenoceptors was also assessed by measuring the noradrenaline (NA)-induced accumulation of [³H]inositol 1-phosphate (IP₁) in brain slices from these animals. No apparent change was observed in the concentration-response relationship between NA and [³H]IP₁ accumulation in rat cerebral cortex after chronic treatment with imipramine. At concentrations higher than 1 M in vitro, imipramine and its metabolite, desipramine, produced a concentration-dependent decrease in the [³H]IP₁ accumulation elicited by NA. This inhibitory effect is likely mediated by direct blockade of alpha₁-adrenoceptors by these drugs. As the endogenous drug concentration would not reach 1 M in our preparation, the lack of changes in alpha₁-adrenoceptor response following chronic imipramine treatment are not likely attributable to residual imipramine or desipramine retained in the tissues. In conclusion, the above findings do not support previous suggestions that brain alpha₁-adrenoceptors are upregulated following chronic imipramine administration.