Martin Hichens

Effects of enalapril, a new converting enzyme inhibitor, in hypertension

The new angiotensin converting enzyme inhibitor enalapril maleate was given in single oral doses of 2.5, 5, and 10 mg to 11 hospitalized patients with uncomplicated essential hypertension who were on a 150‐mEq sodium diet. All doses of enalapril induced reduction of mean seated diastolic blood pressure (SDBP). The magnitude of the initial SDBP reduction was not dose related, but the duration of effect was longer (>12 hr) after the 5 and 10 mg. After dosing, mean plasma angiotensin converting enzyme activity (ACE) and aldosterone concentration (PAC) fell, while plasma renin activity (PRA) rose. Serum concentrations of the active diacid form of enalapril increased linearly with dosage; ACE was inhibited maximally at concentrations above 10 ng/ml. During repeated dosing in the outpatient trial there was attenuation of the antihypertensive effect (12 to 24 hr after dosing) in eight of 10 patients. Despite dose increases only two patients achieved SDBP control (≤90 mm Hg). In the five patients in whom 50 mg/day hydrochlorothiazide was added near the end of the trial mean SDBP was further reduced. Enalapril was well tolerated. Further studies of the drug, especially in combination with diuretic, are needed.

PGF2α-induced loss of corpus luteum gonadotrophin receptors

Abstract In experiments in vivo and in vitro we have previously shown that PGF 2α directly antagonized the action of gonadotrophins on the corpus luteum. To determine if this action of PGF 2α may occur as a consequence of an induced loss of gonadotrophin receptors, binding of hCG to rat luteal tissue was measured following PGF 2α treatment in vivo . In immature rats which were treated with exogenous gonadotrophin to luteinize the gonads, PGF 2α produced a marked and highly significant decrease in circulating progesterone when administered 24 hours before sacrifice. Although the affinity constant (Ka; 1.2-2 × 10 10 L/M) of the luteal receptor to hCG was not affected, PGF 2α treatment produced a marked fall in the binding capacity of the luteal tissue to hCG. This response was absent, however, when PGF 2α was incubated directly with luteal receptor or administered during early pseudopregnancy when corpora lutea are more resistant to luteolysis. Experiments are in progress to determine if the decrease in capacity of luteal receptors to bind hCG is the mechanism or a consequence of luteolysis produced by PGF 2α .

Dopamine receptor changes in untreated and (+)-PHNO-treated MPTP parkinsonian primates.

Fifteen monkeys (Macaca fascicularis) were utilized in this study. Seven naive animals received no treatment and served as controls. Eight animals were rendered parkinsonian with serial injections of MPTP. Three of the parkinsonian monkeys were treated with (+)-4-propyl-9-hydroxynaphthoxasine [(+)-PHNO], a selective dopamine D2 agonist. (+)-PHNO (2-5 micrograms/kg/h) was administered continuously using subcutaneous osmotic pumps. All animals were given weekly scored neurologic examinations throughout the study. Their movement was quantitated in an activity box. The animals were sacrificed 30-120 days after their last MPTP injection by an overdose of sodium pentobarbital. The brains were removed, frozen and cut into 20-microns sections. The density of D1 and D2 receptors was studied in the basal ganglia of these animals at the level of the anterior commissure. For the D2 assay, total binding was determined using various concentrations of [3H]spiperone in buffer containing 300 nm mianserine. For the D1 assay, total binding was determined using various concentrations of [3H]SCH-23390. Tissue isotope concentration was determined from the autoradiographs. The parkinsonian animals demonstrated 90-97% dopamine depletion in the striatum. There was a 75-90% decrease in free movement in the untreated parkinsonian monkeys and their composite clinical score was 8.9 on a scale of 0-16 (zero being normal). Control monkey scores averaged 0.6. The untreated parkinsonian monkeys demonstrated an increase in the number of D2 sites as compared to controls. This increase was greatest at the lateral putamen. The (+)-PHNO-treated monkeys demonstrated increased activity, a neurologic score of 3.4, and a 40-70% decreased in D2 sites in both caudate and putamen. There was no change in the number of D1 binding sites in both the untreated and the (+)-PHNO-treated parkinsonian monkeys as compared to controls.

Initial Evaluation of Transdermal Timolol: Serum Concentrations and β-Blockade

The serum concentrations and β-blockade after dermal application of timolol ointment were evaluated in six healthy men (21–31 years old; 74–82 kg). Two patches (25 cm2) containing placebo and either 30 (n = 2) or 60 mg (n = 4) timolol base were randomly applied to the chest for 30 h. Serial serum concentrations of timolol were measured by a radioligand receptor assay. Bicycle ergometry, at a predetermined workload, was performed before and at 3, 8, 24, and 48 h after patch application; mean ± SD heart rates (beats/min) at these times were 167 ± 2. 158 ± 7, 125 ± 7, 120 ± 5, and 150 ± 5 (last 3 values: p < 0.05 from pretreatment), and β-blockade was evident in all subjects. Measurable serum concentrations in the therapeutic range were achieved in all subjects. The change in exercise-induced heart rate (y) was closely related to log timolol serum concentration (x) (y = −36 × −5.3: r = −0.92: p < 0.001). Based on the amount of timolol in the residual ointment. 50–60% of the original timolol dosage was delivered from the patch. Skin irritation under the patch compared with placebo was minimal. Further studies are warranted to assess the potential clinical utility of transdermal timolol.

Biological Activities of a New Steroidal Inhibitor of δ4-5α-Reductase

Abstract 17β-N,N-Diethylcarbamoyl-4-methyl-4-aza-5α-androstan-3-one (4-MA), a known 5α-reductase inhibitor, was tested in a variety of bioassays designed to document its endocrinological spectrum. It proved to be a relatively nontoxic compound which showed little or no antifertility activity in either male or female rats, no significant estrogenic, progestational, androgenic, or gonadotropin-inhibiting potency, and it did not affect serum prolactin levels. 4-MA did, however, cause feminization of male fetuses carried by treated pregnant female rats. It also caused a cessation in growth of the ventral prostate and seminal vesicles of young adult male rats. Both the feminization of male fetuses and the inhibition of male sex accessory growth are believed to be a result of the inhibition of 5α-reductase by 4-MA.

Rapid block of gonadotropin uptake by corpora lutea in vivo induced by prostaglandin F2α

Intravenous administration of 125I-hCG to 7-8 day pseudopregnant rats resulted in maximum uptake of radioactivity to corpora lutea 2 hours after treatment. At this time tissue/plasma radioactivity ratios on an equal weight basis were: corpora lutea, 70.2 +/- 12.8; ovarian interstitium, 4.6 +/- 0.2; kidney, 2.2 +/- 0.1. No appreciable uptake was seen by adrenals or liver. Radioactivity in corpora lutea was associated primarily with membranes which sedimented at 2000g and when released by heat it was more than 63% bound to luteal LH receptor preparation in vitro. Radioactivity in renal tissue was associated primarily with the 100,000g supernatant fraction and was bound less than 1% to luteal LH receptors in vitro. PGF2alpha significantly reduced uptake (p less than .001) of 125I-hCG by corpora lutea within 30 minutes (-63%) as well as at 1 (-64%), 2 (-75%), 4 (-68%) and 24 hours (-85%). No clear effect of PGF2alpha on uptake of 125I-hCG by ovarian interstitial tissue was seen. Plasma progesterone was significantly decreased (p less than .001) within 30 minutes (-47%; p less than .01) after PGF2alpha treatment and also at 1 (-65%), 2 (-82%), 4 (-68%) and 24 hours (-92%). Two hours after PGF2alpha treatment the content of progesterone in corpora lutea was depressed (-46%; p less than .001). It is suggested that the rapid inhibition of luteal progesterone production induced by PGF2alpha in vivo occurs through a block in gonadotropin uptake by corpora lutea.

Quantitative autoradiographic determination of angiotensin-converting enzyme (kininase II) binding in individual rat brain nuclei with125I-351A, a specific enzyme inhibitor

We report the localization and characterization of angiotensin-converting enzyme (kininase II) in discrete nuclei from individual rat brains by a quantitative autoradiographic technique coupled to computerized microdensitometry. The enzyme was quantitated by incubation of 16-micron-thick brain sections with 0.07-2 nM of the converting enzyme inhibitor 125I-351A and comparison to 125I-standards. This technique can be applied to the study of other enzymes in single rat brain nuclei.

Serum profiles of luteinizing hormone, progesterone and total estrogens during the canine estrous cycle

Abstract Serum levels of LH, total estrogen and progesterone were measured daily by radioimmunoassay during proestrus, estrus and early diestrus in five beagle bitches. Occurrence of the LH peak relative to the onset of estrus was quite variable ranging from 3 days before to 7 days after the onset of estrus. Serum LH levels were elevated for 3 days with a peak value of 25 ± 2 ng/ml reached 2.4 days after the start of estrus. LH levels were ≤ 2 ng/ml when measured at other times during the estrous cycle. Estrogen titers ranged from 84 ± 39 pg/ml at 9 days before the LH peak to 175 ± 15 pg/ml coincident with the LH peak. A broad estrogen peak was evident beginning 5 days before and continuing for 5 days after the LH peak. An estrogen surge was seen in 4 of 5 dogs immediately preceding or coincident with the LH peak suggesting that LH release in the bitch is triggered by a sharp elevation in estrogen levels. Serum progesterone levels rose from ≤ 5 ng/ml before the LH peak to 46 ± 6 ng/ml 6 days afterwards.

Chemical inhibition of estrus in the beagle.

Abstract Twenty anestrus bitches were dosed orally for 90 days with vehicle or 0.9 mg/kg b.w. of 6,6-spiroethylene-19-nor-spiroxenone. All dogs were due in estrus during the test period based on previous average estrous cycle lengths. Estrus was prevented in 100% of the drug-treated bitches. Eight of ten control dogs came into heat during the test period. Hematological and blood biochemical studies did not show any consistent drug-related anomalies. Uterine biopsies, taken at laparotomy from half the dogs in each group, showed no evidence of cystic endometrial hyperplasia or pyometra. Mammary biopsies were also normal. Functional corpora lutea were observed in two control dogs at laparotomy. These dogs had high serum progesterone levels and a secretory endometrium. Drug-treated dogs had low serum progesterone levels and quiescent ovaries.