The effects of estrogen on cortisol metabolism in female baboons

We examined Cortisol (F) dynamics in female baboons $\text{(Papio anubis)}$ treated with diethylstilbestrol (DES) or estradiol (E₂) and compared values with those previously measured in nonpregnant and pregnant animals. Five regularly menstruating baboons (12–18 kg, BW) were administered 5 mg DES daily via fruit or 0.5 mg E₂/0.1ml oil sc for 30 days. Blood samples, obtained before and after treatment, were assayed for serum F concentrations and serum Cortisol binding capacity (CBC). The metabolic clearance (MCR) and production rate (PR) of F and the catabolism of i.v. administered [³H] F were examined 25 and 30 days after initiation of estrogen treatment. Compared with values in nonpregnant baboons, F metabolism in estrogen treated animals is significantly altered and is characterized by increased formation of unconjugated metabolites, decreased glucuronylation, increased excretion of unconjugated F, cortisone, and highly polar metabolites, and increased CBC. These changes induced by estrogen are similar to those observed in intact pregnant baboons and permit the suggestion that the pattern of F metabolism and the level of CBC in baboon pregnancy are the result of elevated estrogen production.However, estrogen also caused a significant decrease in the MCR and PR of F, parameters which, by contrast, are similar in intact pregnant and nonpregnant baboons. These findings indicate that while estrogen also influences the rate of F clearance and F production, these effects of estrogen are not apparent during pregnancy. Collectively, these findings allow the suggestion that estrogen is a major factor which alters F metabolism and increases serum CBC in baboon gestation. However, additional factors are operative in primate pregnancy which maintain PR and MCR of F at levels similar to those of nonpregnant baboons.     

The production and secretion of cortisol by baboon neonates.

The metabolic clearance rate (MCR), transfer constants (p), production (PR) and secretion (SR) rates of cortisol (F) andrortisone (E) were determined by the continuous infusion of {1,2³H}F and {4-¹⁴C}E into 5 neonates delivered prior to the parturition by cesarean section (164–179 days; term = 184 days) and into 5 newborns delivered spontaneously per vagina at term (166 – 187 days). In spontaneously delivered animals, MCR-E (X ± SE, 34.3 ± 7.0 1/day/kg was greater (P < 0.001) than MCR-F (14.9 ± 1.5 1/day/kg), pF to E (59.7 ± 8.9%) exceeded (P < 0.001) pE to F (17.8 ± 3.0%) and the percentage of F bound to serum proteins other than albumin (57.5 ± 6.2) was greater (P < 0.001) than that of E (27.0 ± 10.3) Although the serum E level (25.6 ± 3.6 μg/100 ml) was similar to that of F (33.5 ± 8.0 μg/100 ml), the PR-E (6.4 ± 1.3 μ/min/kg) was greater (P < 0.001) than PR-F (3.3 ± 0.5 μ/min/kg). Approximately eighty-five percent of the E and 65% of the F produced orginated by secretion.In animals delivered by cesarean section, the serum F concentration (32.4 ± 6.7 μ/100ml), pE to F (13.4 ± 2.8%) pF to E (80.0 ± 12.2%) PR-E (4.5 ± 0.2 μ/min/kg) and SR-E (3.9 ± 0.3 μ/min/kg) were not different from values for spontaneously delivered animals. Serum E levels (35.9 ± 1.6 μ/100 ml) were higher but MCR-F (6.7 ± 0.6 1/day/kg) and MCR-E (18.2 ± 0.41/day/kg) lower in neonates delivered by cesarean section. Serum Cortisol binding capacity (μg F bound/100 ml) was greater (P < 0.025) in neonates delivered by cesarean section (23.6 ± 2.6) than in spontaneously delivered animals (14.4 ± 2.0). As a result of these changes in F and E dynamics, PR-F (1.4 ± 0.3 μ/min/kg) and SR-F (0.9 ± 0.2 μ/min/kg) in neonates delivered by cesarean section were lower (P< 0.01) than corresponding values in spontaneously delivered newborns.It is concluded that the greater F secretion in animals delivered spontaneously than those delivered by cesarean section probably results from increased fetal adrenal 3β-hydroxysteroid dehydrogenase-isomerase activity, which as previously reported, occurs in late gestation in this species.     

Haemodynamics using transthoracic echocardiography in healthy pregnant and non-pregnant baboons (Papio hamadryas)

Background To determine systolic and diastolic function using transthoracic echocardiography in the baboon (Papio hamadryas). Methods Transthoracic echocardiography was performed in eight non‐pregnant female and six pregnant baboons according to American Society of Echocardiography recommendations. Results Haemodynamic measurements were obtained from fourteen baboons. Compared to non‐pregnant baboons, pregnant baboons demonstrated: (mean ± SD, pregnant vs. healthy) increased cardiac output (1615 ± 121 ml/minutes vs. 1317 ± 134 ml/minutes P = 0.001) due to an increased heart rate [120 ± 11 beats per minute (BPM) vs. 105 ± 6 BPM P = 0.018]. The inter‐observer and intra‐observer variability (mean difference ± SD) for the left ventricular outflow tract diameter was 0.05 ± 0.07 cm and 0.01 ± 0.03 cm respectively. There was minimal impact to the animal’s daily activities. Conclusions Transthoracic echocardiography was applicable and reproducible for the assessment of haemodynamics in baboons thus enabling translation of animal results to human studies.     

The extrasplanchnic origin of blood dihydrotestosterone in elderly men

The splanchnic extraction and interconversion of testosterone (T) and dihydrotestosterone (DHT) were studied in 5 elderly men undergoing cardiac catheterization using a constant Infusion of [1,2-³H] testosterone and [4-¹⁴C] DHT. Metabolic clearance rate (MCR), splanchnic extraction (SE), splanchnic clearance (SC), extrasplanchnic clearance (ESC), transfer constant In blood ([P]_BB^T-DHT) and transfer constant across the liver ([P]_BB^T-DHT) were calc?ulated. The MCR^T was 675 ± 108 (mean ± SC) L/day and MCR^DHT was 409 ± 68 L/day. SE^T was 45.9 ± 7.0% and SE^DHT was 18.5 ± 5.4%. When these values are compared with those recently reported by us for normal men, there is a $\text{1}\text{3}$ reduction in SE^T and $\text{1}\text{2}$ reduction for SE^DHT in elderly men. The calculated SC^T and ESC^T were 355 ± 72 L/day and 320 ± 86 L/day, respectively. SC^DHT and ESC^DHT were 145 + 48 L/day and 263 ± 77 L/day respectively, suggesting that a major fraction of DHT is metabolized in extrasplanchnic organs. No evidence for a net appearance of DHT by either mass or specific activity analysis in hepatic vein blood was observed indicating that the splanchnic compartment does not contribute DHT into the circulation either by $\text{de novp}$ synthesis or via conversion from testosterone. This work indicates that conversion of testosterone to DHT in elderly men occurs entirely in extrasplanchnic tissue.     

Fecal steroid analysis of ovarian cycles in free-ranging baboons

This paper reports field and laboratory tests of serial sampling, solid phase extraction, and microradioimmunoassay methods for the collection, preservation, and analysis of fecal steroids. The field study was conducted in a troop of 87 yellow baboons (Papio cynocephalus) in the Tana River Primate Reserve, Kenya. Serial samples of four focal females and opportunistic sampling of 18 additional females over 22 days of sampling yielded a total of 62 samples, X = 3.1 ± 0.4/day, demonstrating the feasibility of regular field collection and extraction. Estradiol and progesterone concentrations in the field-extracted samples exhibited high recovery and statistically significant correlations (P < 0.05) with concentrations in the lab-extracted samples, suggesting that solid phase extraction could provide a useful alternative to freezing in sites where electricity or liquid nitrogen is not available. Tests of microradioimmunoassays demonstrated that these assays were sensitive, accurate, and precise when applied to the assay of fecal extracts, providing estimates of ovarian steroids that varied significantly with reproductive state. The demonstration that testosterone could be accurately and reliably assayed in fecal extracts suggests that these techniques also could be applied to the study of male reproductive function. Parallels between fecal profiles of cycling and pregnant baboons with patterns reported for serum steroids in baboons suggest that fecal steroids might be useful in distinguishing amenorrhea from early pregnancy in free-ranging baboons as well as in species lacking external indices of reproductive state. © 1995 Wiley-Liss, Inc.     

Elimination kinetics and protein binding of theophylline in the rabbit

The detailed elimination kinetics of theophylline were studied in 27 rabbits. Each received a 10 mg/kg intravenous bolus of aminophylline. The theophylline half-life ($\text{T}\text{1}\text{2}$) was 3.8 ± 0.63 hr. The apparent volume of distribution (V_D) and total body clearance (TBC) for theophylline were 439 ± 60 ml/kg and 81.0 ± 17.3 ml/kg·hr respectively. Theophylline protein binding was determined in 10 animals. The mean bound fraction was 74.3 ± 3.9% (range, 68.3–78.0%); the fraction bound was concentration indifferent over a serum concentration range of 5–20 μgm/ml.     

The in vivo metabolism of progestins: IV. the metabolic clearance rate and plasma binding of 6α-methylpregn-4-ene-3,20-dione in women

[³H]6α-methylprogesterone (6MP) was synthesized by selective catalytic tritiation of the Δ¹-olefinic bond of 6α-methylpregna-1,4-diene-3,20-dione. The metabolic clearance rate of 6MP (MCR⁶MP) was determined in 6 women by the single injection technique. The plasma MCR^6MP was 4047 ± 298 L/day (59 ± 15 L/day/kg) which was higher than the MCR of progesterone and medroxyprogesterone acetate (6α-methyl-17α-hydroxy-pregna-4-ene-3,20-dione acetate). The high clearance was not due to binding or metabolism of 6MP by red cells. Although 6MP was bound to CBG with a lower affinity than progesterone, this could not entirely explain the high MCR^6MP. When considered with the reports of progesterone and medroxyprogesterone acetate clearance, the present studies suggest that the 6α-substitution of progesterone leads to an increased rate of steroid metabolism in women.     

Direct estimation of urine estrone conjugate for a rapid pregnancy diagnosis in sows

A rapid and direct radioimmunoassay of urine estrone conjugate (E₁C) was developed. Urine samples were taken from Large White sows by inserting sponges in the vagina which were expelled during micturition. Analysis of samples collected daily from 13 sows between 2 and 40 days after service showed that high urine E₁C levels occurred between day 20 and 30 after insemination in pregnant sows; maximum concentrations were observed on day 25 (79.4 ± 11.7 ng/ml, $\text{X}\text{± s.e.m.}$). In this period E₁C levels never exceeded 1 ng/ml in nonpregnant sows. A single urine sample was then taken from 84 sows, 25 days after insemination, to check the accuracy of E₁C estimation as a test for early pregnancy diagnosis. Seventy-six of the examined animals were correctly diagnosed, giving an overall accuracy of 90.4%. No relationship was found between litter size and urine E₁C levels.     

Zinc and copper concentrations in serum from Spanish women during pregnancy

A cross-sectional study of serum zinc (Zn) and copper (Cu) levels in 31 healthy pregnant women and 51 healthy, nonpregnant controls living in the Mediterranean area of Granada, Spain, was performed. The subjects were divided into two groups: Group A, consisted of pregnant women in three categories according to the trimester of pregnancy, and Group B consisted of nonpregnant women acting as controls. In pregnant women, serum Zn levels were found from 0.300-1.340 mg/L and serum Cu from 0.936-2.304 mg/L, whereas in the nonpregnant women group, the mean serum levels were 0.947 ±0.265 mg/L for Zn and 1.092 ±0.365 mg/L for Cu. Serum Zn progressively decreased with gestation. Mean Zn levels were 0.829 ±0.253, 0.846 ±0.329, and 0.620 ±0.142 mg/L, corresponding to the first, second, and third trimesters of pregnancy, respectively. Serum Zn concentrations were significantly lower in pregnant women as compared to controls: 0.712 ±0.236 mg/L vs 0.947 ±0.265 mg/L, respectively (p < 0.05). In contrast, Cu levels increased with period of gestation from 1.053 ±0.498 mg/L in the first trimester to 1.616 ±0.304 mg/L in the second and 1.689 ±0.344 mg/L in the third. Serum Cu levels in the second and third trimesters of pregnancy were significantly higher (p < 0.05) than those determined during the first trimester and for nonpregnant controls. Both Zn and Cu during pregnancy did not appear to be dependent on the subject’s age (p > 0.05).     

The utilization of placental substrates for cortisol synthesis by the baboon fetus near term

We have determined the proportion of the invivo cortisol (F) secretion rate (SRF) derived from circulating pregnenolone (P5) and progesterone (P4) in 9 baboon (Papiopapio) neonates, 5 (4 ♂, 1 ♀) delivered prior to the onset of labor by cesarean section (CS, 164–179 days) and 4 (2 ♂ , 2 ♀) delivered spontaneously at term (SD, 164–179 days; term = 184 days). The metabolic clearance rate (MCR; 1/d/kg) and production rates (PR; mg/d/kg) of P4 and P5 and transfer constants (p) for the reactions P5 → P4₁₄ P5 → F, and P4 → F, were determined by continuous infusion of [1,2-³H] P5 and [4-¹⁴C] P4.In CS animals the MCR-P5 (41.4 ± 5.6; X ± SE) was lower than the MCR-P4 (74.0 ± 8.5; P < 0.001). However, the pP5 → F (1.0% ± 0.3%) and pP4 → F (0.9% ± 0.3%) were similar although lower (P < 0.001) than pP5 → P4 (9.0% ±1.4%). The PR-P4 (7.0 ± 0.8) was 4–5 times greater than the PR-P5 (P < 0.01). In SD newborns, only the pP5 → F (3.4% ± 0.9%) and the PR-P4 (0.5 ± 0.2) were different (P < 0.01) from values in CS neonates. These results indicate that although the baboon fetus has the capacity to convert P5 to P4, the abundant quantities of P4 measured in fetal serum (95 ± 12 ng/ml) near term are primarily placental in origin. Moreover, the apparently low (< 5%) transfer constants for the conversion of P5 or P4 to F suggests minimal utilization of these circulating precursors for F synthesis. Indeed, the calculated proportion of the SR-F derived from circulating P4 was 5.3% ± 2.0% in CS neonates and only 0.3% ± 0.1% in SD newborns. In these animals, values for the utilization of circulating P5 were 1.4% ± 0.4% and 1.6% ± 0.4%, respectively.We conclude that endogenous adrenal substrates and not placental substrates are the primary precursors utilized for fetal adrenal F production in late baboon gestation.     

Effects of neurotrophic stress on maternal metabolism and binding of plasma cortisol in late pregnant guinea-pigs and their fetuses

The maternal metabolic clearance rate (MCR) and the binding of cortisol in the plasma of fetus and mother were estimated 8 days before term in conscious pregnant guinea-pigs, control or subjected to a neurotrophic stress (they were immobilized for 3 h in a dark room in front of an intermittent luminous flash). The maternal MCR of cortisol dropped during pregnancy related to an increase in corticosteroid binding globulin (CBG) and the stress mimicked these changes with a decrease in MCR and a rise in CBG. The increase in cortisol concentrations occurring in the fetal plasma after maternal stress could be related to the increase in free cortisol in the stressed mother. Nevertheless, although the fetal CBG did not rise after maternal stress, the increase in free cortisol in the fetal plasma remained moderate, due to the numerous free sites of CBG and albumin for cortisol.     

Effects of exogenous prostaglandin-F2α (PGF2α) on pregnancy status in white-tailed deer

As part of a study to develop contraceptive methods for white-tailed deer (Odocoileus virginianus), it was necessary to terminate pregnancies in some does. The abortifacient chosen was PGF_2α. At 76 days or less of gestation, PGF_2α administration (10 mg i.m.) did not decrease mean serum progesterone (P) concentrations, and only one doe of 13 aborted. Re-administration of PGF_2α (15 mg i.m.) on approximately day 97 of gestation (21 days after the first injection) did not alter mean serum P concentrations 6 days postinjection, and only one doe of 11 aborted. A third injection of PGF_2α (25 mg i.v.) on approximately day 113 of gestation (16 days after the second injection) tended to decrease mean P concentrations by 1.4 ng/ml 2 days following treatment, and no doe of 11 aborted. A fourth injection of PGF_2α (50 mg i.m.) on approximately day 124 of gestation (11 days after the third injection) decreased mean P concentrations by 2.9 ng/ml 2 days following treatment (P < 0.05), and two of 11 does aborted. Finally, a combination of 50 mg PGF_2α and 15 mg betamethasone was administered i.m. to the remaining pregnant does on approximately day 140 of gestation (16 days after the fourth injection). Mean serum P concentrations decreased from 4.8 ± 0.4 ng/ml to 0.7 ± 0.2 ng/ml 3 days postinjection, a mean decrease of 4.1 ng/ml (P < 0.05). This treatment induced abortion in five of seven does. These data suggest that PGF_2α alone, at a dose that causes luteolysis and pregnancy termination in cows and goats, does not do so in pregnant white-tailed deer. However, a combination of betamethasone and PGF_2α may prove to be an effective lu-teolytic agent or abortifacient for white-tailed deer. © 1994 Wiley-Liss, Inc.     

Erythrocyte metallothionein in relation to other biochemical zinc indices in pregnant and nonpregnant women

Erythrocyte metallothionein (E-MT) is considered a promising index of zinc status in humans, since it may be more sensitive than other biochemical indices to changes in dietary zinc. However, conditions of high zinc demand with substantial redistribution of tissue zinc and specific changes in hormone profile, such as pregnancy, may have an influence on E-MT levels in addition to dietary zinc. In this study, we compared E-MT concentrations in relation to other biochemical zinc indices in healthy pregnant women at delivery (n=40) and nonpregnant women (n=22) with similar habitual dietary zinc intakes (average 13.3 mg/d). Pregnant women had lower serum zinc and albumin-bound serum zinc, but higher levels of {ie115-1}-macroglobulin-bound serum zinc than the nonpregnant women. Erythrocyte zinc (E-Zn) was similar in both groups, but E-MT (mean±SE) was slightly but significantly (p<0.05) higher in the pregnant women (2.9±0.09 nmol/g protein) compared to nonpregnant women (2.6±0.06 nmol/g protein). A significant correlation was observed between E-MT and E-Zn in the nonpregnant women (r=0.70;p<0.001), consistent with the role of intracellular zinc in the regulation of metallothionein synthesis. However, such correlation was not observed in the pregnant women, suggesting that E-MT levels in pregnancy may be influenced by factors related to the pregnant state.     

Kinetics of testosterone metabolism in normal postmenopausal women and women with breast cancer

The constant infusion and single injection techniques were utilized to study the kinetics of ³H-testosterone (T) metabolism in postmenopausal women with and without breast cancer. The metabolic clearance rates (mean ± SEM) for normal postmenopausal women were $\text{578 ± 82}\text{and}\text{644 ±128}\text{1}\text{24}\text{h}$ as obtained by the constant infusion and single injection techniques, respectively. The corresponding results for the women with breast cancer (patients) are $\text{644 ± 25}\text{and}\text{617 ± 106}\text{1}\text{24}\text{h}$. The single injection technique yielded values for rate constants (units) and volumes of distribution (1); k₁ = 37.5 ± 1.6 for the normals and 34.5 ±1.9 for the patients. K₂ = 76.6 ± 5.1 for the normals and 71.1 ± 1.6 for the patients, V₁ = 7.9 ± 2.2 for the normals and 8.7 ± 1.4 for the patients and V₂ = 7.0 ± 1.5 for the normals and 6.4 ± 1.2 for the patients. The constant infusion technique yielded values for the conversion ratios for the transformation of T to several products; 4-androstene-3,17-dione/T of 0.02 ± 0.003 for normals and 0.03± 0.002 for patients, 5α-dihydrotestosterone/T of 0.02 ± 0.002 for normals and 0.03 ± 0.002 for patients, estrone/T of 0.04 ± 0.01 for normals and 0.04 ± 0.01 for patients, estradiol-17β/T of 0.02 ± 0.005 for normals and 0.03 ± 0.005 for patients and estrone sulfate/T of O.16 ± 0.02 for normals and 0.24 ± 0.06 for patients. The T plasma concentrations and production rates were similar for the two groups of subjects. Hence there were no significant differences between the normals and the patients for all the kinetic parameters. It was determined that all the estradiol being produced in postmenopausal women could be coming from circulating T.     

Multiple ovulation resulting from low level administration of PMSG to cattle at different stages of the oestrous cycle

Two experiments were carried out to determine whether differences in sensitivity to exogenous gonadotrophin which exist during the oestrous cycle can be used effectively in the induction of multiple pregnancy in cattle. In Experiment I, Hereford heifers and cows were injected with 800 IU pregnant mare serum gonadotrophin (PMSG) on approximately day 10 of the oestrous cycle, followed 48 h later by 30 mg prostaglandin F_2α (PGF_2α). Controls were treated with PGF_2α alone. Mean ovulation rates based on rectal palpation were 1.33 ± 0.10 (range: 1–2) and 3.05 ± 0.68 (range: 1–13) for 21 control and 21 treated animals, respectively (P < 0.02). In Experiment II, Hereford cows were treated with 800 IU PMSG on either day 5 (14 cows) or day 10 (12 cows) of the oestrous cycle, followed 48 h later by PGF_2α. Mean numbers of ovulations for animals that became pregnant were 1.50 ± 0.26 (range 1–3) and 3.80 ± 0.74 (range 1–7), respectively (P < 0.02). A high incidence of embryonic wastage occurred by 120 days of gestation in animals treated on day 10. The results of this study indicate that taking advantage of an animal's reduced responsiveness to exogenous gonadotrophin during the early portion of the oestrous cycle may be useful in developing methods for inducing multiple births with exogenous gonadotrophins.     

In vitro synthesis of progesterone and prostaglandin F by luteal tissue and prostaglandin F by endometrial tissue from the pig

The relationship between progesterone (P₄) synthesis $\text{in vitro}$ by luteal tissue and prostaglandin F (PGF) synthesis $\text{in vitro}$ by endometrium and luteal tissue from two stages of the cycle, Days 7 to 8 and 15 to 16, was determined. Luteal and endometrial tissues were collected from pigs in three experimental groups at two stages of the cycle: (A) 6 pigs on Days 7 to 8 with spontaneous, 5 to 6 day old corpora lutea (CL); (B) 5 pigs on Days 15 to 16 with spontaneous, 13 to 14 day old CL; and (C) 6 pigs on Days 15 to 16 with spontaneous, 13 to 14 day old CL and 5 to 6 day old CL induced by pregnant mares serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG) injections. Pigs with spontaneous, 13 to 14 day old CL of the cycle and PMSG-HCG induced accessory, 5 to 6 day old CL were used so that P₄ and PGF synthesis in tissue from old and new CL could be compared in the same pig on Day 15 to 16 of the cycle. Tissues (100 mg minces) were incubated in 5 ml of Krebs Ringer solution in an atmosphere of 95% 0₂:5% CO₂ for 2 hours at 0° C, 37° C, or 37° C with 1.3 x 10^?4M indomethacin (IND). An aliquot of the incubation medium and an aliquot of the supernatant after homogenization of the tissue in the remaining medium of each flask was quantified for P₄ and PGF by radioimmunoassay. P₄ and PGF release into the medium and total accumulation of P₄ and PGF in the flasks indicated that $\text{de novo}$ synthesis had occured at 37° C. Compared to tissue from 13 to 14 day old CL, tissue from 5 to 6 day old CL synthesized more P₄ per flask (53.9 $\text{vs}$ 25.0 ng/mg tissue, P<.001) and released more P₄ into the medium (20.8 $\text{vs}$ 8.8 ng/mg, P<.001). P₄ synthesis by luteal tissue from 5 to 6 day old and 13 to 14 day old CL from pigs in group C was similar to P₄ synthesis by luteal tissue from pigs in group A and group B, respectively. Luteul PGF synthesis was not affected significantly by either the age of the CL or by PMSG-HCG treatment. For endometrial samples, the synthesis of PGF was not significantly different among pigs in groups A, B and C. If uterine PGF is involved in luteal regression in the pig, the sensitivity of the CL to PGF may be more important than an increase in PGF secretion during the late luteal phase of the estrous cycle.     

Effect of metabolic acidosis on phosphate transport by the renal brush-border membrane

Metabolic acidosis produces a phosphaturia which is independent of parathyroid hormone or dietary phosphorus intake. To study the underlying mechanism, inorganic phosphate (P_i) and glucose transport were studied in brush-border membrane vesicles prepared from the renal cortex of parathyroidectomized rats gavaged for three days with either 7.5 ml of 1.6% NaCl (control) or 1.5% NH₄Cl (acidosis). At killing, blood pH and plasma bicarbonate were $\text{7.36 ± 0.01}$ and $\text{21.8 ± 0.8}\text{mequiv./l}$, respectively, in control and $\text{7.12 ± 0.03}$ ($\text{P < 0.01}$) and $\text{11.1 ± 1.2}$ ($\text{P < 0.01}$) in acidotic rats. Serum P_i was similar in both groups, while 24 h urine P_i excretion was higher in the acidotic group ($\text{P < 0.01}$). Peak sodium-dependent uptake of P_i, measured after 1.5 min of incubation, was higher in controls than acidotic rats ($\text{4442 ± 464}$ vs. $\text{2412 ± 259}\text{pmol/mg}$ protein, $\text{P < 0.01}$), whereas peak glucose uptake at 1.5 min was not significantly different between the groups. Equilibrium values for P_i and glucose uptake were similar in the two groups. $\text{K}{}_{\mathrm{<mtext>m</mtext>}}$ for P_i uptake in the control and acidotic animals were not different, 0.036 and 0.040 mM, respectively. By contrast, $\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ was higher in controls than in the acidotic group, 3.13 vs. 1.15 nmol/mg protein per 15 s. These results suggest that metabolic acidosis directly inhibits P_i uptake by the brush border of the proximal tubule by decreasing the availability of P_i carriers of the renal brush-border membrane.     

Pharmacokinetic study of exogenously administered ß-endorphin using a rapid radioreceptor assay in rats

A rapid radioreceptor assay for measuring ß-endorphin (ß-EP) in unextracted serum has been developed. The method is based upon the inhibition by ß-EP of ³H-naloxone binding to the specific receptors on rat brain membranes, prepared in a stable form of pellets. Effect of serum on the assay was minimized by adding pooled serum to the equal dilution of total serum in the assay mixture. Pharmacokinetic analysis of pharmacologically active ß-EP equivalents (ß-EP eq.) in rats was performed using this method. The serum disappearance of ß-EP eq. after iv administration followed a biexponential decline and pharmacokinetic parameters were calculated by a two-compartment open model. The half-lives of α-phase and ß-phase were 2.6 ± 0.5 min and 6.2 ± 1.6 hr (mean ± SE; n=6), respectively. The volume of the central compartment (V₁) and that of steady-state (Vd_ss) were 67 ± 16 and 480 ± 75 ml/kg (mean ± SE; n=6), respectively. The total body serum clearance (CL_tot) was 2.1 ± 0.9 ml/min/kg (mean ± SE; n=6). The serum disappearance curve of ß-EP eq. obtained in the present study was similar to that previously reported by Houghten et al. (Proc. Natl. Acad. Sci. U.S.A. $\text{77}$, 4588–4591 (1980)), in which the disapperance of total radioactivity of tritiated ß-EP in rats was examined.     

Anatomical and enzymic studies of leaves of a C3 × C4Flaveria F1 hybrid exhibiting reduced photorespiration

Flaveria pringlei exhibits C₃ CO₂ compensation concentration (Г) values averaging 53 μl CO₂/l at 21% (v/v) O₂ and 25 ± 2°C. When this species is hybridized with the C₄ species, F. brownii (male) ($\text{Г = 6 μ}\text{l CO}{}_2\text{/}\text{l}$), the F₁ hybrid plants exhibit an average Г value of 31 μl CO₂/l at 21% O₂.Although light micrographs of leaf cross-sections show that the leaves of the hybrid plants possess the mesophyll arrangement characteristic of F. pringlei leaves, the hybrid plants have some bundle-sheath chloroplasts. However, the numbers of these organelles do not appear to be intermediate with respect to the numbers in the parents and are closest to the small number present in the bundle-sheath cells of F. pringlei leaves. The activities of key C₄ enzymes (in μmol · mg Chl^?1 · h^?1) are: phosphoenolpyruvate (PEP) carboxylase, 121; pyruvate, orthophosphate (P_i) dikinase, 26; NADP-malate dehydrogenase, 2529; and NADP-malic enzyme, 82. All of these activities are substantially higher than in F. pringlei, but are only 7–10% of those in F. brownii (with the exception of the NADP-malate dehydrogenase activity). These data suggest that a C₄ cycle might be operating to a limited extent in the hybrid plants resulting in reduced photorespiration.Whether or not C₄ photosynthesis occurs in these hybrid plants, they represent the first reported C₃ × C₄ F₁ hybrids to exhibit reduced Γ-values. This cross and its reciprocal should be useful models for studying the anatomical and biochemical factors determining the development of limited C₄ photosynthesis in C₃ species.