Changes In Secretion Rate Research Articles

Variation in maternal lactation practices associated with changes in diurnal maternal inflammation

While the importance of human milk in shaping infant immune function is well established, the impact of at-the-nipple (ATN) breastfeeding on maternal immune status has been understudied. Since lactation evolved to support infant survival and boost maternal fitness, we predict that ATN breastfeeding will confer benefits on maternal immune function. We measure the absolute and relative frequency of different infant feeding methods (ATN breastfeeding, pumping, donated milk, other supplementation) used by postpartum women in Seattle, WA (USA). We implement Bayesian modeling to estimate the effects of ATN breastfeeding on diurnal change in secretion rate of “pro-inflammatory” salivary cytokines and C-reactive protein (CRP). Our results show that most mothers in our sample used a variety of infant feeding methods, with pumping as the most common alternative to ATN breastfeeding. We find that ATN breastfeeding is associated with non-linear effects on diurnal IL-8 and CRP. Furthermore, we find that women who report zero versus ubiquitous ATN breastfeeding exhibit opposing diurnal patterns in CRP secretion rate. This study provides evidence that variation in maternal lactation practices corresponds to differences in maternal immune responses, highlighting how measuring lactation as a continuous variable can further enhance understanding of postpartum maternal physiology.

The Effects Of Cardiorespiratory Fitness On Changes In Salivary Immunoglobulin A (siga) Following Maximal Exercise

Salivary immunoglobulin A (SIgA) levels are recognized as a physiological marker of the health of the human mucosal immune system. Previous research has shown SIgA concentrations decrease immediately following high intensity and long duration exercise while moderate intensity exercise may result in an increase in SIgA levels. More recently, researchers have suggested that a person’s cardiorespiratory fitness (CRF) may impact SIgA response following acute exercise. PURPOSE: To investigate the effect of CRF on SIgA changes following maximal exercise. METHODS: Unstimulated saliva was collected from twenty-three (5 males, 18 females) healthy college students (mAge = 20.1 ± 1.2) before and 5 minutes after a VO2max test. Samples were measured for volume to determine salivary flow rate (SFR). Biochemical analysis was performed using an enzyme-linked immunosorbent assay (ELISA) to determine absolute SIgA concentrations. Additionally, SIgA secretion rate was computed from SFR and absolute SIgA concentrations. A median split was performed to establish a higher fitness group (HF) and a lower fitness (LF) group. RESULTS: The HF group (m = 50.8 mL·kg-1·min-1) was significantly different than the LF group (m = 38.2 mL·kg-1·min-1), t(21) = 4.67, p < .001. No differences were determined between changes in SIgA concentrations of the HF group (m = 398.9 μg·mL-1) and the LF group (m = 278.3 μg·mL-1). Moreover, there was no difference in changes in secretion rate between the HF (m = 148.1 μg·min-1) and LF (m = 175.5 μg/min) groups or SFR for the HF (m = -72.29 μg·min-1) and LF (m = 58.58 μg·min-1) groups. CONCLUSION: Cardiorespiratory fitness does not appear to affect the concentration, secretion rate or salivary flow rate of SIgA following maximal exercise.

Omega-3 fatty acid ethyl ester supplementation decreases very-low-density lipoprotein triacylglycerol secretion in obese men

Dysregulated VLDL-TAG (very-low-density lipoprotein triacylglycerol) metabolism in obesity may account for hypertriacylglycerolaemia and increased cardiovascular disease. ω-3 FAEEs (omega-3 fatty acid ethyl esters) decrease plasma TAG and VLDL concentrations, but the mechanisms are not fully understood. In the present study, we carried out a 6-week randomized, placebo-controlled study to examine the effect of high-dose ω-3 FAEE supplementation (3.2g/day) on the metabolism of VLDL-TAG in obese men using intravenous administration of d5-glycerol. We also explored the relationship of VLDL-TAG kinetics with the metabolism of VLDL-apo (apolipoprotein) B-100 and HDL (high-density lipoprotein)-apoA-I. VLDL-TAG isotopic enrichment was measured using gas chromatography-mass spectrometry. Kinetic parameters were derived using a multicompartmental model. Compared with placebo, ω-3 FAEE supplementation significantly lowered plasma concentrations of total (-14%, P<0.05) and VLDL-TAG (-32%, P<0.05), as well as hepatic secretion of VLDL-TAG (-32%, P<0.03). The FCR (fractional catabolic rate) of VLDL-TAG was not altered by ω-3 FAEEs. There was a significant association between the change in secretion rates of VLDL-TAG and VLDL-apoB-100 (r=0.706, P<0.05). However, the change in VLDL-TAG secretion rate was not associated with change in HDL-apoA-I FCR (r=0.139, P>0.05). Our results suggest that the TAG-lowering effect of ω-3 FAEEs is associated with the decreased VLDL-TAG secretion rate and hence lower plasma VLDL-TAG concentration in obesity. The changes in VLDL-TAG and apoB-100 kinetics are closely coupled.

Involvement of adipose tissues in the early hypolipidemic action of PPARγ agonism in the rat

Agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma) are insulin sensitizers that potently improve lipemia in rodents. This study aimed to determine the contribution of lipid secretion vs. clearance and the involvement of white adipose tissue (WAT) and brown adipose tissue (BAT) in the rapid hypolipidemic action of PPARgamma agonism. Male rats were treated with rosiglitazone (RSG; 15 mg x kg(-1) x day(-1)) for 1 to 4 days, and determinants of lipid metabolism were assessed postprandially. Serum triglycerides (TG) were lowered (-54%) after 3 days of RSG treatment, due to accelerated clearance from blood without contribution of changes in secretion rates. Both BAT and WAT were the major sites of RSG action on TG clearance, the increase in TG-derived fatty acid (FA) uptake reaching threefold in BAT and 60-90% in WAT depots. Accelerated TG clearance was associated with increased lipoprotein lipase (LPL) activity mostly in BAT. Serum nonesterified FA were lowered (-20%) by a single dose of RSG, an effect associated with increased expression levels of FA binding/transport (fatty acid binding protein-4), esterification (diacylglycerol acyltransferase-1), and recycling glycerol kinase and phosphoenolpyruvate carboxykinase enzymes in BAT and WAT, suggesting FA trapping. After 4 days of RSG treatment, nonesterified fatty acid (NEFA) uptake was also stimulated in both BAT (2.5-fold) and WAT (40%). These findings demonstrate the causal involvement of increased efficiency of LPL-mediated TG clearance and reveal the important contribution of TG-derived and albumin-bound FA uptake by BAT in the rapid hypolipidemic action of PPARgamma agonism in the rat.

Major Advances Associated with Environmental Effects on Dairy Cattle

It has long been known that season of the year has major impacts on dairy animal performance measures including growth, reproduction, and lactation. Additionally, as average production per cow has doubled, the metabolic heat output per animal has increased substantially rendering animals more susceptible to heat stress. This, in turn, has altered cooling and housing requirements for cattle. Substantial progress has been made in the last quarter-century in delineating the mechanisms by which thermal stress and photoperiod influence performance of dairy animals. Acclimation to thermal stress is now identified as a homeorhetic process under endocrine control. The process of acclimation occurs in 2 phases (acute and chronic) and involves changes in secretion rate of hormones as well as receptor populations in target tissues. The time required to complete both phases is weeks rather than days. The opportunity may exist to modify endocrine status of animals and improve their resistance to heat and cold stress. New estimates of genotype×environment interactions support use of recently available molecular and genomics tools to identify the genetic basis of heat-stress sensitivity and tolerance. Improved understanding of environmental effects on nutrient requirements has resulted in diets for dairy animals during different weather conditions. Demonstration that estrus behavior is adversely affected by heat stress has led to increased use of timed insemination schemes during the warm summer months to improve conception rates by discarding the need to detect estrus. Studies evaluating the effects of heat stress on embryonic survival support use of cooling during the immediate postbreeding period and use of embryo transfer to improve pregnancy rates. Successful cooling strategies for lactating dairy cows are based on maximizing available routes of heat exchange, convection, conduction, radiation, and evaporation. Areas in dairy operations in which cooling systems have been used to enhance cow comfort, improve milk production, reproductive efficiency, and profit include both housing and milking facilities. Currently, air movement (fans), wetting (soaking) the cow's body surface, high pressure mist (evaporation) to cool the air in the cows’ environment, and facilities designed to minimize the transfer of solar radiation are used for heat abatement. Finally, improved understanding of photoperiod effects on cattle has allowed producers to maximize beneficial effects of photoperiod length while minimizing negative effects.

Deconstructing Milk Yield and Composition During Lactation Using Biologically Based Lactation Models

A recently developed biological model of lactation described changes in daily milk yield throughout lactation as the result of 3 processes, secretory cell differentiation, cell death, and secretion rate per cell. This paper extends the model to describe the production of milk components (fat, protein, lactose, and water) throughout lactation by replacing milk secretion rate of the original model with the secretion rates of the four components. The milk component model approach was used to examine the relationship between milk yield and the major determinants of its production, using the secretion of milk components throughout lactation. Newly derived models were tested on 461 lactations from a single Holstein herd and used to estimate variability of secretion rates throughout lactation. Because the pattern of cell numbers throughout lactation is not precisely known, an alternative pattern of cell numbers was modeled and the concomitant change in secretion rates outlined. Fat secretion rate was the most variable, as measured by its weekly coefficient of variation throughout lactation. Secretion rates of lactose and water were nearly constant throughout lactation and highly correlated (0.94). Fat and protein secretion rates also were well correlated (0.53). The known biochemistry of milk component production related well to the secretion rate observations derived from the model. Lactose secretion rate and numbers of active secretory cells primarily determined daily milk yield.

Stable isotope turnover of apolipoproteins of high-density lipoproteins in humans

Amino acid precursors labelled with stable isotopes have been successfully used to explore the metabolism of the apolipoproteins of HDL. Some methodological and mathematical modelling problems remain, mainly related to amino acid recycling in a plasma protein such as apolipoprotein A-I with a long residence time (the reciprocal of the fractional catabolic rate) of 4-5 days. Apolipoprotein A-I, apolipoprotein E, and apolipoprotein A-IV in triglyceride-rich lipoproteins (containing chylomicrons, VLDL, and remnants) exhibit more complex kinetics. The small amounts of apolipoprotein A-I and of apolipoprotein A-IV in the triglyceride-rich lipoproteins have a residence time similar to that of the apolipoprotein A-I of HDL. In contrast, the apolipoprotein E in triglyceride-rich lipoproteins has been found to have an average residence time of 0.11 days. Diets low in saturated fat and cholesterol, which lower HDL levels, do so by decreasing the secretion of apolipoprotein A-I, with apolipoprotein A-II kinetics unaffected. Individuals with impaired glucose tolerance have a decreased residence time of apolipoprotein A-I but no change in secretion rate or in apolipoprotein A-II kinetics. This suggests a link between insulin resistance and the risk of atherosclerosis. In heterozygous familial hypercholesterolemia, both the fractional catabolic rate and the secretion rate of apolipoprotein A-I are increased, resulting in no change in the plasma level. Stable isotope studies have strengthened the evidence that triglyceride enrichment of HDL increases its catabolism Laboratory.

Age-related changes in salivary antibodies to commensal oral and gut biota.

The prevalence of mucosally derived infections appears to increase with age, suggesting dysfunction at the mucosal surfaces. The present investigation was undertaken to examine any age-related changes in secretion rates and concentrations of secretory antibodies in whole and parotid saliva in a healthy adult population. A total of 116 subjects were subdivided into the following age groups: 20-39 years, 40-59 years, 60-79 years and 80 years and over. Specific immunoglobulin A (IgA), IgG and IgM antibodies in whole and parotid saliva to Streptococcus mutans (serotype c), Actinomyces viscosus NCTC 10951, and Escherichia coli NCTC 10418 were quantified by enzyme-linked immunosorbent assay. IgA antibodies to all three organisms examined increased with age in both whole and parotid saliva, whereas IgG antibody levels to S. mutans in whole saliva were significantly decreased with age. IgG antibodies to E. coli in parotid saliva were reduced in older age groups. IgM antibody levels to S. mutans were reduced with age in both secretions, whereas IgM antibodies to A. viscosus were greatest in the oldest age groups. No significant changes with age were observed in salivary IgM antibody levels to E. coli. No significant reduction in the secretion rates of IgA antibodies were observed in parotid or whole saliva, whereas IgG and IgM antibody secretion rates to all three microorganisms were reduced in most age groups in both whole and parotid saliva. The results of this investigation have demonstrated age-related changes with salivary antibodies, but, whereas salivary IgG and IgM antibodies showed decreases, salivary IgA levels generally increased with age. This suggests that the ability to form IgA antibody responses is not impaired with increased age, and that secretion rates and functional properties of antibodies may be as important as concentrations in protection against mucosal infective diseases.

Changes in the secretion rate and production of colostrum by ewes over the first 24 hpost partum

AbstractAn experiment was conducted to examine the changes in colostrum secretion rate and colostrum composition in ewes over the first 24 h post partum. Sixteen mature Suffolk × Cambridge ewes, which had produced one to four lambs, were used. Colostrum yield was estimated within 1 h of parturition and colostrum secretion rate measured between 3 and 6 h, 9 and 12 h, 15 and 18 h and 21 and 24 h post partum. Samples of colostrum were taken at each milking and the composition analysed. The mean yield (g) of colostrum at 1 h was 801 (s.d. 568·9) with a range from 35 to 2450 g. Mean secretion rates, in g/h, at 3 to 6 h, 9 to 12 h, 15 to 18 h and 21 to 24 h were 120 (s.d. 67·0), 104 (s.d. 55·2), 112 (s.d. 49·8) and 109 (s.d. 41·1) respectively. At 1 h, mean concentrations, in g/l, of total solids, fat, protein, ash and IgG were 367 (s.d. 76·9), 132 (s.d. 43·7), 203 (s.d. 43·2), 9.6 (s.d. 2·4) and 116 (s.d. 30·2) respectively. Corresponding values at 24 h were 242 (s.d. 38·8), 122 (s.d. 39·5), 71 (s.d. 11·2), 6.8 (s.d. 1·0) and 15 (s.d. 12·5).Sequential samples were taken throughout the milking process within 1 h of paturition from a further eight Dorset-cross ewes. There were no significant differences in the composition of colostrum due to stage of milking, although there was a suggestion that fat content was higher in the final sample than the first (140·1v.104·1 g/l, P = 0·084). It is clear that there is a large amount of variation in the secretion rate and composition of colostrum produced by ewes over the first 24 h post partum. However, a single sample taken between 3 and 12 h post partum would be a good indicator of 24 h yield (r = 0·88) and composition (total solids, r = 0·90 and IgG, r = 0·93).

Age-related changes in secretion rate and post-secretory metabolism of growth hormone in swine

The effect of age on growth hormone (GH) metabolism and GH-releasing factor (GRF)-induced GH concentrations were studied in 7 young (3 mo, 39 kg) and 7 old (30 mo, 156 kg) Yorkshire x Landrace female pigs. Jugular catheters were surgically inserted and 60 hr later total serum volume was determined. The following day, all animals were infused for 3 hr with GH (30.3 ng·min/kg B.W.) in order to calculate GH metabolic clearance rate (MCR), secretion rate (SR) and half-life ( t 1 2 ). Two days later, 15 μg/kg of GRF was injected i.v. into all pigs. On a per animal basis, aging increased (P<.01) MCR (299 vs 132 ml/min), SR (714 vs 422 ng/min) and serum volume (6.6 vs 2.0 l), whereas t 1 2 was unaltered (P>.1). Basal GH concentrations were lower in older pigs (P<.10) but the GRF-induced GH concentrations (measured as GH peak or area under the curve, AUC) were not affected by age (P>.1). Yet, when induced total GH secretion (AUC × MCR) and average total serum GH (mean GH post-injection x serum volume) were calculated per pig, these variables significantly increased between 3 and 30 mo of age. Basal IGF-I concentrations were lower in older pigs (P<.01), yet, there was a tendency (P = .10) for these pigs to show a greater IGF-I response to GH infusion. The present data therefore indicate that age alters both SR and post-secretory metabolism of GH. Since GRF-induced GH concentrations and post-secretory metabolism of GH are not altered similarly by age, both these variables must be considered when describing GH responses of swine.

Dental caries and salivary and microbial conditions in 50–60‐year‐old persons

In a group of 124 persons, 50-60 yr old, the prevalence at baseline of mutans streptococci (MS) and lactobacilli and the salivary secretion rate and buffer capacity were examined. The mean secretion rate was 1.58 mL/min with a flow rate below 1 mL/min found in 20% of the persons. A buffer capacity below end pH 5.5 was observed in 64% of the subjects. MS was not detected in 5% of the persons whereas 17% had 10(6) or more MS per ml saliva. Lactobacilli were not found in 10% of the persons while 21% had counts in excess of 10(5) CFU mL. A new examination 5 yr later in 1986 revealed no significant changes in secretion rate and buffer capacity or in the population of lactobacilli, whereas markedly elevated levels of salivary MS were found. S. sobrinus was detected in 35-37% of the persons at the two examinations. Persons with both S. mutans and S. sobrinus had more MS than persons with only S. mutans.

Effect of sorbitol- and xylitol-containing chewing gum on salivary microflora, saliva, and oral sugar clearance.

The effect of frequent use of a sorbitol-containing nicotine chewing gum on saliva secretion rate and buffer capacity and some oral bacteria was studied in 27 patients at a smoking cessation clinic. The effect was compared with that obtained after frequent use of a chewing gum containing xylitol in a second study in 14 subjects. The results showed that sorbitol-containing nicotine chewing gum had no significant effect on salivary numbers of oral streptococci and lactobacilli during a 3-month period of active chewing five times a day. Chewing on xylitol-containing gum caused a significant decrease in salivary S. mutans after 2 months but not after 3 months. No change in secretion rate or buffer capacity was observed in the two studies. Oral sugar clearance time was reduced after 3 months with a statistically significant difference to baseline values in subjects consuming the sorbitol-containing nicotine chewing gum.

Effects of maternal nutrition and plasma progesterone concentrations on survival and growth of the sheep embryo in early gestation

SUMMARYMature Merino ewes (n = 320) were fed either maintenance (100% M) or 25% maintenance (25% M) rations from the day after mating until embryos were collected at either day 11 or 21 after mating. On the 4th day after mating 223 ewes were ovariectomized and given 5, 10, 15, 20 or 25 mg progesterone/day (intramuscular) until embryo collection. A further group of sham operated ewes (n = 54) acted as controls. Despite live-weight losses of 10·7 and 15·8% from mating to days 11 and 21 after mating respectively, ewes on 25% M rations showed no evidence that embryonic survival was influenced by undernutrition. The embryos from ewes fed 25 % M rations were significantly (P &lt; 0·05) smaller than those fed 100% M (crown-rump measurements were 5·93 ± 0·139 mm and 6·39 ± 0·116 mm at day 21 after mating in the 25 % M and 100% M groups respectively). Development, assessed by formation of the first pharangeal lobe and the fore- and hind-limb buds, was significantly retarded (P &lt; 0·05) in the 21-day-old embryos from the undernourished ewes. Embryo survival in ovariectomized ewes receiving 5 or 10 mg progesterone/day was significantly (P &lt; 0·05) lower than in ovariectomized ewes receiving 20 and 25 mg progesterone/ day at day 11 after mating. Embryo survival at both days 11 and 21 after mating increased with increasing doses of progesterone. Ewes fed 25% M rations had elevated (P&lt; 0·001) concentrations of peripheral progesterone compared with those fed 100% M. This occurred when the progesterone was derived from either exogenous or endogenous (ovarian) sources, dismissing the possibility that changes in secretion rates could account for these observed differences. Differences in embryo growth and development were not related to these variations in the plasma progesterone concentration. Undernutrition restricted both growth and development to 21 days of pregnancy.

Gonadotropin-releasing hormone receptors: characterization, physiological regulation, and relationship to reproductive function.

THE TONIC and cyclic secretion of gonadotropins is mediated by the hypothalamic production of gonadotropin releasing hormone (GnRH). The direct assessment of hypothalamic function has been hampered by the absence of reliable methods for the measurement of GnRH production and secretion. Endogenous hypothalamic GnRH probably never reaches the general circulation in sufficiently high concentration to be measured by RIA (1–5), since the pituitary gland has the capacity to metabolize the majority of the peptide secreted into the hypothalamo-hypophyseal portal circulation (6–10). Attempts to determine the rate and amplitude of GnRH secretion have shown that GnRH concentrations in hypophyseal stalk plasma fluctuate between 20 and 800 pM (11–14). Such studies have revealed that GnRH is released in a pulsatile fashion, although rapid changes in secretion rate cannot be detected during the long period required for sample collection. In addition to modulating the concentration of GnRH in hypophyseal portal plasma (14–16), the sex-steroid milieu of the animal may also regulate the frequency of GnRH pulses.

Sigmoidal relationship between parathyroid hormone secretion rate and plasma calcium concentration in calves.

Parathyroid hormone (PTH) secretion rate was measured in 16 anesthetized calves by using a technique involving radioimmunoassay of parathyroid venous blood which was collected during timed intervals and measured volumetrically. The calves ranged in age from 2-14 weeks. Plasma calcium concentration was altered by infusion of solutions of CaCl2 or disodium ethylenediamine tetracetate (Na2 EDTA) into the jugular vein. When plasma calcium concentrations exceeded 10.5 mg/100 ml, a basal, non-suppressible secretion rate of 0.3 ng/kg/min was maintained despite the induction of hypercalcemia. Slight changes in secretion rate were observed in response to changes of plasma calcium in the range between 9 and 10.5 mg/100 ml. Below 9 mg/100 ml, a small decrease in plasma calcium concentration evoked a pronounced increase in secretion rate. A maximal secretion rate of about 5.5 ng/kg/min was attained at a plasma calcium concentration of approximately 7.5 mg/100 ml and it was not increased by more severe hypocalcemia. These observations confirm the sigmoidal relationship between PTH secretion rate and plasma calcium concentration which was previously suggested by measurement of PTH concentration in peripheral plasma of hypocalcemic, parturient cows.

Gastric emptying and secretion in the rhesus monkey.

The volume and composition of the gastric contents as well as the rates of gastric emptying and secretion were determined simultaneously in conscious chair-adapted monkeys. These determinations were made during fasting and after a liquid meal, thereby allowing studies of the physiologic variables which regulate gastric emptying and gastric secretion. Administration of a water meal is followed by a complex pattern of changes in rates of secretion as well as the fractional rate of emptying. During administration of a 100-ml water meal (pH 7.4), intragastric volume increased while acid concentration decreased; both then returned to fasting values 50 min later. The fractional rate of emptying increased fivefold during administration of the water meal, returned to basal values after 30 min, and then increased again, indicating that gastric emptying cannot be characterized as a simple first-order process with a constant coefficient. The pattern of the change in the rate of water secretion was similar to that for fractional gastric emptying. In contrast, after the meal, gastric acid secretion increased steadily and did not become maximal until 20 min.

Compartmental arrangement of steroid precursors and the control of steroid hormone secretion in rat adrenal tissue in vitro.

ABSTRACT Using a technique of incubation with dialysis, capsules (zona glomerulosa) and inner zone preparations of adrenal tissue from control, cortisol treated and Frusemide treated rats have been studied. The formation of corticosterone, deoxycorticosterone and 18-hydroxydeoxycorticosterone from both endogenous precursors and from added [14C] progesterone was examined. In the inner zone incubations from control and cortisol treated rats, products from the two precursor types appeared to be quite miscible as judged by their dialysability. Cortisol treatment depressed the formation of all three products from endogenous precursors, while their formation from [14C] progesterone was unaffected. These findings are consistent with the conventional view of the major point of action of ACTH at a stage preceding pregnenolone formation. In contrast, the formation of corticosterone from endogenous precursors in the capsule was specifically depressed by cortisol treatment. The formation of deoxycorticosterone and 18-hydroxydeoxycorticosterone was unaffected; the yields of all three compounds from [14C] progesterone was also unaffected. At the same time the dialysibility of the material formed from endogenous precursors was greatly reduced, while the dialysibility of the radioactive products was unchanged. In the Frusemide treated animals, capsule incubations showed no changes in formation of steroids from either precursor type and the miscibility of the steroid from the two sources was unaffected. In the inner zone incubations the formation of deoxycorticosterone and corticosterone was increased from both precursors, while the formation of 18-hydroxydeoxycorticosterone was reduced from endogenous precursors and unchanged from [14C] progesterone. Dialysibility of the steroids was unaffected by these procedures. The results suggest that various mechanisms may operate to allow independent variations in secretion rates of compounds occurring after the point of pregnenolone formation – normally held to be the major point of ACTH action. In particular it appears that, when ACTH secretion is suppressed, steroid formed from endogenous precursors may become attached to a non-dialysable component in the capsule of the gland. It is an attractive hypothesis that this renders the steroid less vulnerable to 11β-hydroxylation although it remains vulnerable to 21- and 18-hydroxylation. This mechanism is not observed if products from [14C] progesterone are studied alone. Treatment with Frusemide shows that other mechanisms may also allow differential changes in secretion rates of the three compounds. These mechanisms await elucidation.

18-Hydrocorticosterone Biosynthesis in an Aldosterone Secreting Tumor and in the Surrounding Nontumorous Adrenal Gland

A greater than normal concentration of aldosterone has been found in adrenal tumors from patients with primary aldosteronism (1). 18-Hydroxycorticosterone is probably an intermediary product in the conversion of corticosterone to aldosterone (2). This conversion takes place in the zona glomerulosa. The parallel changes in secretion rates of aldosterone and 18-hydroxycorticosterone which have been observed in man under a variety of conditions support the intermediary role of 18-hydroxycorticosterone (3). However, 18-hydroxycorticosterone is also synthesized in the fasciculata-reticularis zones of the cow adrenal gland (4), and to a lesser degree, in the inner zones of the rat adrenal gland (5).The present report describes the conversion of corticosterone-4-14C to 18-hydroxycorticosterone and aldosterone by an aldosterone producing tumor and the surrounding nontumorous adrenal tissue. Only the mitochondrial fraction of both tissues contained converting activity. The tumor converted 4 times more corticostero...

Measurement of insulin secretion. A review of current methods.

The principal methods currently used to measure insulin secretion are briefly reviewed. From observed changes in concentration of immunoreactive insulin in plasma, insulin secretion in vivo can be more accurately assessed and smaller changes in secretion rate detected using pancreatic rather than systemic venous samples of blood. Measurement of secretion in vitro is complicated by the release from acinar tissue of a substance which destroys secreted insulin and similar polypeptides but whose action can be reduced or circumvented. When interpreting the effects of stimulants and inhibitors, it has also to be remembered that they could act indirectly through their actions upon other tissues of the body or upon cells other than the beta-cells of the pancreatic islets. These and other factors should be taken into account when interpreting data obtained by the several practical methods now used to study the insulin secretory process.

Anatomical changes in middle ear and cochlea of the rat following stimulation with high intensity sound.

SummaryRats were exposed to sound of 200–220 cps at an intensity of 130–135 db for 2, 12 or 48 hours. A marked increase in secretion of corticosterone was observed after 2 or 48 hours, and a marked decrease after 12 hours. Significant anatomical changes were not observed in the middle ears or cochleas of any of the animals. The data suggest that the changes in secretion rate of corticosterone do not depend on anatomical changes in the rat cochleas.