Torcetrapib-induced blood pressure elevation is independent of CETP inhibition and is accompanied by increased circulating levels of aldosterone.

BACKGROUND AND PURPOSE: Inhibition of cholesteryl ester transfer protein (CETP) with torcetrapib in humans increases plasma high density lipoprotein (HDL) cholesterol levels but is associated with increased blood pressure. In a phase 3 clinical study, evaluating the effects of torcetrapib in atherosclerosis, there was an excess of deaths and adverse cardiovascular events in patients taking torcetrapib. The studies reported herein sought to evaluate off-target effects of torcetrapib. EXPERIMENTAL APPROACH: Cardiovascular effects of the CETP inhibitors torcetrapib and anacetrapib were evaluated in animal models. KEY RESULTS: Torcetrapib evoked an acute increase in blood pressure in all species evaluated whereas no increase was observed with anacetrapib. The pressor effect of torcetrapib was not diminished in the presence of adrenoceptor, angiotensin II or endothelin receptor antagonists. Torcetrapib did not have a contractile effect on vascular smooth muscle suggesting its effects in vivo are via the release of a secondary mediator. Treatment with torcetrapib was associated with an increase in plasma levels of aldosterone and corticosterone and, in vitro, was shown to release aldosterone from adrenocortical cells. Increased adrenal steroid levels were not observed with anacetrapib. Inhibition of adrenal steroid synthesis did not inhibit the pressor response to torcetrapib whereas adrenalectomy prevented the ability of torcetrapib to increase blood pressure in rats. CONCLUSIONS AND IMPLICATIONS: Torcetrapib evoked an acute increase in blood pressure and an acute increase in plasma adrenal steroids. The acute pressor response to torcetrapib was not mediated by adrenal steroids but was dependent on intact adrenal glands.

Vascularization of the adrenal cortex: its possible involvement in the regulation of steroid hormone release.

This review examines the morphology of the adrenal gland with particular reference to the adrenal vasculature. It examines the possibility that variability in adrenal gland responsiveness may be attributable to neural or hormonal modulation of adrenal blood flow. Changes in the rate of blood flow through the adrenal cortex would be expected to play an important role in the regulation of steroid hormone release. It would affect both the delivery of the major stimulant (ACTH) and the removal of the end product from the steroidogenic cells (the glucocorticoids). In the past, interest in this area has concentrated on the regulation of arterial blood flow, rather than the regulation of venous drainage. The current review examines the concept of vascular damming, and attempts to link the morphological features of the gland with experimental data associated with glucocorticoid release. It is postulated that regulation of venous drainage, via the vascular dam, plays an important role in the storage of the secretory product during the animals' inactive phase, and in the initial rapid rise in plasma levels of the glucocorticoids seen in response to stress or injection of ACTH.

Diurnal variation in adrenal gland freshweight due to vascular damming: a possible role in corticosterone storage.

Previous in vitro studies have disclosed the existence of a diurnal variation in adrenal gland freshweight in the minimally stressed rat (inactive phase freshweight > active phase freshweight). In the present study this active/inactive phase difference in adrenal weight was examined using light microscopy, transmission electron microscopy (TEM) and backscattered scanning electron microscopy (BSEM). Morphological and stereological examination of the resultant micrographs has shown a significant increase in gland cross-sectional width in the active phase, localised to the zona fasciculata/reticularis region of the cortex. However, TEM examination of cells from this region, comparing volume and surface densities from active and inactive phase glands, has not provided evidence of a diurnal variation in cell size. Analysis of the BSEM investigation of vascular, cellular and interstitial compartments of the glands confirmed the absence of variation in the cellular compartment but showed a diurnal variation in the vascular compartment of the zona fasciculata/reticularis. The circadian related changes in vascular volume density begin at the cortico-medullary border where greatest difference is observed between the active and inactive phases. This difference continues throughout the zona fasciculata/reticularis decreasing in size as it approaches the zona glomerulosa region. These findings are explained in terms of the existence of a cortico-medullary vascular dam that is a possible contributor to the rapid steroidogenic response seen on initial stimulation of the gland by adrenocorticotrophic hormone (ACTH).

A circadian rhythm in adrenal responsiveness to ACTH is not confirmed by in vitro studies.

From in vitro studies a circadian variation in adrenal gland response to ACTH was observed. Regulation of this circadian rhythm in adrenal responsiveness was localized to the cellular level; involving variation in either receptor density or affinity. In the present study the circadian variation in adrenal gland responsiveness was studied using an in vitro approach. Levels of corticosterone secretion during the active and inactive phases were determined using incubated rat adrenal slices in the presence and absence of submaximal stimulation by the synthetic ACTH peptide, ACTH(1-24). Initially, a circadian difference in adrenal responsiveness appeared to exist in all groups except the betamethasone pretreated. However, data expressed in terms of corticosterone secretion/mg adrenal weight proved to be misleading due to the presence of an apparent circadian pattern in adrenal gland weight; the adrenal glands from animals in the dark being significantly less in weight than those from animals in the light phase. When the data were expressed in terms of actual gland output, no circadian variation in adrenal response to exogenous ACTH(1-24) stimulation was apparent. In conclusion, the present study does not support the concept of a circadian variation in the adrenal response to ACTH(1-24) stimulation resulting from a variation in the responsiveness of the adrenal cells themselves. However, the present study does not preclude the possibility of a circadian variation due to modulation of adrenal responsiveness by humoral factor(s) other than ACTH.

Reversal of the effects of aging in soybean seeds.

Accelerated aging predisposed seeds to imbibition injury. Slowing the rate of hydration prevented the loss of germinability due to imbibition injury. Germinability of accelerated aged seeds (50 hours) was increased from 10 to 90% by controlling the rate of imbibition. Slow hydration also prevented seed electrolyte leakage. This may indicate that cell membrane permeability or rupture was a major factor contributing to the loss of germinability after aging.Reversal of the effects of aging (repair) was accomplished by slowly inbibing and then redrying seeds (priming). This treatment lowered steep water conductivity by a factor of 2 to 5. Priming also increased the per cent germination of low vigor seeds. The mechanism of this reversal was probably metabolic because it depended on temperature, seed moisture, and treatment duration.Priming doubled the survival of seeds in the accelerated aging vigor test. The ;rejuvenation' was accepted as evidence for metabolic repair. Since the ;vigor' of seeds was increased by priming, metabolic repair probably included other subcellular components as well as the plasma membrane.

Peripheral reticulum in chloroplasts of plants differing in CO2 fixation pathways and photorespiration.

The development of peripheral reticulum (PR) in chloroplasts varies in C3 and C4 plants. In general, PR is more extensive in C4 plants, but PR is also seen in the chloroplasts of some C3 plants. Within some C4 plants, PR is seen in the bundle sheath cells which predominantly use the C3 pathway. Thus, PR is not associated directly with the presence of the C4 pathway on a cellular basis. Its predominance in C4 plants must be related to some characteristic other than the method of CO2 fixation. Ultrastructural evidence suggests that PR is associated with the rapid transfer of substances into and out of chloroplasts and from mesophyll to bundle sheath cells.

The association of chloroplast peripheral reticulum with low photorespiration rates in a photorespiring plant species.

A peripheral reticulum occurs in mesophyll chloroplasts of the pentose cycle plantDactylis glomerata L. (orchardgrass). This structural feature was previously thought to occur primarily in the chloroplasts of tropical grasses and other species utilizing the C4-dicarboxylic-acid photosynthesis pathway. Since the peripheral reticulum is seen in a selection ofD. glomerata which has a low rate of photorespiration, but not in a selection which has a high rate of photorespiration (Carlsonet al., 1971), photorespiratory rates may be dependent in part on the presence or absence of a chloroplast peripheral reticulum.

Leaf microbodies (peroxisomes) and catalase localization in plants differing in their photosynthetic carbon pathways.

The tropical grasses sugarcane (Saccharum officinarum) and pangolagrass (Digitaria decumbens) contained fewer leaf microbodies than temperate orchardgrass (Dactylis glomerata). Leaf microbodies were seen in both the mesophyll and bundle sheath cells of tropical grasses. The fibrous elements in the microbodies of tropical grasses differed from those of the temperate grass. Catalase was predominantly localized in the microbodies of leaf cells (3,3'-diaminobenzidine method). The site of greatest catalase activity appeared to be the fibrous and/or crystalline inclusions within the microbodies. The low rates of photorespiration noted in tropical grasses do not appear to be due to the complete absence of the necessary organelles.

Starch accumulation associated with growth reduction at low temperatures in a tropical plant.

Growth of Digitaria decumbens is severely reduced by night temperatures of 10 degrees C or below. Ultra-structure of leaves and chemical analyses show a high starch content in chloroplasts of plants illuminated and kept at a temperature of 30 degrees C. This starch disappears after a period in the dark at 30 degrees C, but it remains if the temperature during the dark period is 10 degrees C. The inhibition or slowing of starch translocation out of chloroplasts appears to account for reduced photo-synthesis and growth at low night temperatures.

Detached leaves: Renewed potential for growth.

Leaves of Portulaca oleracea that had reached full size on the parent plant showed as much as a four-fold increase in growth when detached and rooted in nutrient solution. Neither addition of indoleacetic acid nor variations in the nutrient concentrations had an effect on the growth rate. Root formation which was necessary to initiate renewed growth of the leaf occurred only in nutrient solution.

Effects of Phosfon-S on Nucleic Acid Metabolism in Pisum sativum Alaska.

Phosfon-S, a substance which inhibits stem elongation, alters nucleic acid metabolism in Pisum sativum Alaska. Methylated albumin kieselguhr (MAK) columns were used to fractionate (32)P-labeled nucleic acids. Phosfon-S treatment of the plants resulted in a decrease in soluble RNA and an increase in ribosomal RNA. Specific activities of the various nucleic acid fractions were lower as a result of treatment. The nucleic acids from treated tissues were more resistant to RNase degradation, and endogenous RNase activity was lower in treated tissues. When RNase treated nucleic acids were fractionated on MAK columns, the DNA-RNA fractions from treated plants had a higher specific activity than that of the control, which was not true before nuclease treatment. Spectrophotometric examination of this fraction revealed a difference in absorption spectra, possibly indicating a Phosfon-S nucleic acid complex. It is suggested that these alterations in nucleic acid metabolism could in turn alter a wide variety of metabolic processes, resulting in retarded growth.