Corticosteroid control of distal nephron sodium handling, particularly through the amiloride-sensitive sodium channel (ENaC), has a key role in blood pressure regulation. The mechanisms regulating ENaC activity remain unclear. Despite the generation of useful mouse models of disorders of electrolyte balance and blood pressure, there has been little study of distal nephron sodium handling in this species. To investigate how corticosteroids regulate ENaC activity we isolated cDNA for the three mouse ENaC subunits (alpha, beta and gamma), enabling their quantitation by competitive PCR and in situ hybridisation. Kidneys were analysed from mice 6 days after adrenalectomy or placement of osmotic mini-pumps delivering aldosterone (50 microg/kg per day), dexamethasone (100 microg/kg per day), spironolactone (20 mg/kg per day) or vehicle alone (controls). In controls, renal ENaCalpha mRNA exceeded beta or gamma by approximately 1.75- to 2.8-fold. All subunit mRNAs were expressed in renal cortex and outer medulla, where the pattern of expression was fully consistent with localisation in collecting duct, whereas the distribution in cortex suggested expression extended beyond the collecting duct into adjacent distal tubule. Subunit mRNA expression decreased from cortex to outer medulla, with a gradual reduction in beta and gamma, and ENaCalpha decreased sharply ( approximately 50%) across the outer medulla. Expression of ENaCbeta and gamma (but not alpha) extended into inner medulla, suggesting the potential for inner medulla collecting duct cation channels in which at least ENaCbetagamma participate. Aldosterone significantly increased ENaC subunit expression; the other treatments had little effect. Aldosterone caused a 1.9- to 3.5-fold increase in ENaCalpha (particularly marked in outer medullary collecting duct), but changes for beta and gamma were minor and limited to the cortex. The results raise the possibility that medullary ENaCalpha upregulation by aldosterone will create more favourable subunit stoichiometry leading to a more substantial increase in ENaC activity. In cortex, such a mechanism is unlikely to have a major role.

Tumor necrosis factor-α (TNFα) is a cytokine with multiple biological functions which, in mammals, has been shown to modulate muscle and adipose tissue metabolism. In fish, TNFα has been identified in several species. However, few studies have examined the role of TNFα in fish outside the immune system. In this study, we assessed the effects of human recombinant TNFα and conditioned media from rainbow trout lipopolysaccharide (LPS)-stimulated macrophages (LPS-MCM) on lipolysis in isolated rainbow trout adipocytes. Furthermore, we studied the effects of an LPS injection in vivo on lipid metabolism. In our study, human recombinant TNFα stimulated lipolysis in trout adipocytes in a time- and dose-dependent manner. Similarly, LPS-MCM stimulated lipolysis in trout adipocytes when compared with control conditioned medium. Experiments using specific inhibitors of the MAP kinase pathway showed that p44/42 and p38 are partially involved in the lipolytic effects of TNFα. On the other hand, adipocytes from LPS-injected rainbow trout showed higher basal lipolysis than adipocytes from control fish after 24 h, while this effect was not seen at 72 h. Furthermore, lipoprotein lipase (LPL) activity in adipose tissue of LPS-injected fish was lower than in the controls at 24 h. These data suggest that TNFα plays an important role in the control of lipid metabolism in rainbow trout by stimulating lipolysis in vitro and in vivo and by down-regulating LPL activity of adipose tissue in vivo.

Urine for the analysis of pregnanediol was collected weekly for 3 months from 209 menstruant women aged 11–24 years who lived with their parents and from 59 women aged 17–23 years who had left the parental home. Menstrual cycles were classed as ovulatory if the 24-h pregnanediol output in the 12 days preceding menstruation was ≥ 5 μmol on a single occasion or if the total excreted on 2 days, 1 week apart, was ≥ 7 μmol.

In the first group, ovulatory incidence increased with menarchal age. Unfailing ovulation occurred in 22·9, 25·0,44·8,42·9, 63·2, 71·8 and 82·6% of those who were < 1, 1−<2, 2−<3, 3−<4, 4−< 5, 5–8 and 9–12 years from menarche. Comparable figures for the women who lived in flats and hostels were 40·0% (menarchal age, 5–8 years) and 78·6% (9–12 years).

It is concluded that a regular pattern of ovulatory menstrual cycles is established in most young women within 5 years of the menarche, and that departure from the family home is often associated with a regression to a juvenile pattern of anovulatory menstrual cycles.

ABSTRACT

A study was conducted to investigate developmental patterns of plasma concentrations of insulin-like growth factor-I (IGF-I), body growth and body composition in mice from lines selected for seven generations on the basis of low (L) or high (H) plasma IGF-I, and in a random-bred control (C) line. Litter size was standardized to eight individuals with equal sex ratios (as far as possible) within 48 h of birth. Pups were weaned at an average of 21 days and separated on the basis of sex. Blood samples were collected from one male and one female of each litter on days, 21, 42, 63 and 105 for analysis of plasma concentrations of IGF-I. The animals were then killed and analysed for water, fat and crude protein content.

The plasma concentration of IGF-I was influenced by line (P<0·05) but not by sex. Significant (P< 0·001) differences in liveweight between mice from L and H lines were first evident at 21 days of age. From 28 until 105 days of age the H line was significantly (P< 0·001) heavier than both L and C lines, but differences between C and L lines were inconsistent and mostly non-significant. The growth velocity of the H line was significantly greater than that of C or L lines between 14 and 42 days of age, but differences in growth velocities of C compared with L lines were generally non-significant.

Nose–anus length was significantly (P<0·01) affected by sex and line from 42 to 105 days of age, but anus–tail length was not affected by sex or line at any age. Effects of sex and line on empty (digesta-free) body weight and wet weights of carcass and skin plus viscera fractions followed a pattern similar to those of liveweights. The effects of sex and line on protein, water and fat content also paralleled their effects on body size. Differences between males and females, and between the lines, in amount of protein, water and fat could be entirely accounted for by the corresponding differences in body weight.

It is concluded from these results that divergent selection on the basis of plasma IGF-I at 42 days of age resulted in lines of animals differing in plasma IGF-I from 21 days of age until maturity. These divergent concentrations of IGF-I are associated with differences between the lines in body growth, particularly during the period of accelerated growth at puberty, but not with changes in body composition.

Journal of Endocrinology (1990) 124, 151–158

ABSTRACT

Phosphoinositide hydrolysis is important in mediating the actions of oxytocin and prostaglandin (PG) F_2α on uterine contractions during labour. We have measured the effect of oxytocin, PGF_2α and other agents on the formation of inositol phosphates (IPs) in cultured human myometrial cells labelled with [³H]inositol and on changes in intracellular free Ca²⁺ concentration ([Ca^{2 +} ]_i) in cells loaded with Fura-2.

Oxytocin induced the formation of [³H]IPs in a concentration-dependent manner with an EC₅₀ (concentration of agonist producing 50% of the maximal response) of 1·4 ±0·5 nmol/l (mean ± s.e.m.). The maximal response was obtained with 1 μmol oxytocin/l and represented a stimulation of 670% over basal. PGF_2α also stimulated the formation of [³H]IPs and the response at 1 μmol/l was a 204% stimulation over basal. The effects of PGF_2α were independent of extracellular Ca^{2 +} but the effect of oxytocin was reduced with low extracellular Ca^{2 +}. Cyclic AMP formation, induced by forskolin or PGE₂, had no effect on the stimulated levels of [³H]IPs. Pertussis toxin (PT) reduced the oxytocin-stimulated formation of [³H]IPs in a concentration-dependent manner. The maximal effect of PT resulted in an 80% reduction in the formation of [³H]IPs. However, PGF_2α stimulation was not affected by PT treatment.

To analyse the action of PT further, we studied its effect on oxytocin-induced changes in [Ca^{2 +} ]_i. The basal [Ca^{2 +}]_i was 112 ±4 nmol/l (n=225 cells) and was not affected by PT treatment (109 ± 3 nmol/l; n= 200 cells). In the absence of PT, 1 μmol oxytocin/l increased [Ca^{2 +} ]_i to a peak of 522 ±26 nmol/l, and in PT-treated cells, the [Ca^{2 +} ]_i peak was reduced to 348 ± 16 nmol/l. Similar inhibitory effects of PT were obtained at oxytocin concentrations ranging from 1 to 100 nmol/l.

Our data suggest that in human myometrial cells, the oxytocin-induced production of [³H]IPs and increase in [Ca^{2 +} ]_i are mediated by a PT-sensitive G-protein. However, a significant fraction of the oxytocin response appears to be mediated by a PT-insensitive G-protein, possibly a member of the G_q family.

Journal of Endocrinology (1993) 136, 497–509

SUMMARY

This study has shown that corpora lutea, stromal tissue and corpora albicantes from human ovaries contain prostaglandin E (PGE) and PGF_α, and that the two former tissues can synthesize these prostaglandins during incubation. Enhanced synthesis, especially of PGE, occurred on adding arachidonic acid to the incubation medium, and the presence of prostaglandin synthetase activity was conclusively demonstrated.

In corpora lutea obtained during the early and mid-luteal phase, the mean concentrations of PGE and PGF_α were 34·3 and 9·6 ng/g respectively (mean ratio PGE:PGF_α = 3·7); similar values were found in three corpora lutea from women at 10–12 weeks of pregnancy. All these corpora lutea contained appreciable amounts of progesterone and oestradiol-17β. Prostaglandin levels were generally lower in corpora lutea obtained during the late luteal phase, although the PGE:PGF_α ratio had increased to a mean value of 8·4. In corpora albicantes, the concentrations of both PGE and PGF_α were significantly higher than the levels found in corpora lutea (P < 0·01), whilst the mean ratio of PGE:PGF_α had fallen significantly to 1·8 (P < 0·01). Prostaglandin levels in stromal tissue varied considerably between individuals. The mean values were significantly lower than those of the corpora albicantes (P < 0·01) but not significantly different to corpora lutea at any stage.

These findings are discussed in relation to the possible role of prostaglandins in ovarian steroidogenesis and corpus luteum regression in man.

ABSTRACT

Angiotensin II and I significantly raised potassium and lowered sodium and chloride ion concentrations in arterial plasma, with peak changes occurring in the first 2 min of a 6-min infusion period. The octapeptide increased the arterial K⁺ level in a dose-dependent manner, but the response showed tachyphylaxis when multiple infusions of 6-min duration were administered after a recovery interval of only 5 min. Raising the arterial blood pressure by 20–33 mmHg with adrenaline and noradrenaline failed to account for the increase in arterial plasma K⁺ concentration produced by the two peptides. These findings, in particular the rise in K⁺ concentration, are discussed in relation to possible mechanisms by which angiotensin II affects arteriolar tone.

J. Endocr. (1985) 104, 143–148