The ability of parathyroid hormone (PTH) to enhance bone formation has recently been exploited in the treatment of osteoporosis. However, the underlying mechanisms are unknown. Osteoblasts, the bone-forming cells, derive from multipotential bone marrow stromal precursors called colony-forming units-fibroblastic (CFU-F) upon culture ex vivo. Adhesion of such stromal precursors to bone is likely to be an early event in the anabolic response of bone to PTH. To test this, we measured the number of CFU-F that could be extracted from murine bone marrow after administration of an anabolic dose of PTH. We found that a very early response is a dramatic reduction, starting within 2 h, in the number of CFU-F that could be extracted from their bone marrow. We then tested whether PTH has the ability to activate adhesion of CFU-F in vitro. For this, bone marrow cells were incubated in PTH for varying times. Non-adherent cells were then removed, and the adherent cells were incubated in PTH-free medium for 14 days to assess, as colony formation, the number of CFU-F that had adhered in the preceding period. We found that incubation in PTH caused a substantial increase in the number of CFU-F that adhered within 24 h. This increase was abrogated by peptidic inhibitors of integrins. The increase did not seem to be mediated through a PTH-induced increase in interleukin-6, since interleukin-6 had no effect on CFU-F numbers when substituted for PTH. Similarly, adhesion was unaffected by incubation of bone marrow cells in dibutyryl cyclic AMP, nor by inhibitors or donors of nitric oxide. However, activation of CFU-F in vitro by PTH was strongly inhibited by indomethacin and mimicked by prostaglandin E(2), and indomethacin reversed the PTH-mediated reduction of CFU-F that could be extracted from mouse bone marrow. These results suggested that PTH rapidly activates adhesion of CFU-F to plastic or bone surfaces. This activation may represent an early event in the anabolic response of bone cells to PTH.
J Davies and TJ Chambers
D. T. DAVIES and J. COLLINS
After the i.m. injection of 10 μg synthetic LH releasing hormone (LH-RH) into Japanese quail the levels of LH and FSH in plasma rose significantly within 2 min. The increased level of LH declined rapidly but that of FSH was maintained for the duration of the experiment. To determine whether the anterior pituitary gland is primed by LH-RH a double injection schedule was adopted. It would appear that, while endogenous LH-RH may prime the avian pituitary gland slightly, synthetic LH-RH is ineffective.
I. J. DAVIES and K. J. RYAN
[7-3H]Pregnenolone was incubated with homogenates of adrenal glands from two 100-day-old sheep foetuses. Cortisol and corticosterone were isolated and identified by reverse isotope dilution and recrystallization to constant specific activity. Together these two compounds accounted for 12% and 17% of the substrate with the two tissue preparations. Other C21 and C19 metabolites which were sought were not present in appreciable quantities. Additional incubations were done with the adrenals of lamb foetuses ranging in age from 110 days of gestation to the immediate newborn period. Glucocorticoidogenic capacity similar to that of the 100-day-old foetuses was demonstrated throughout this period and no age-related change was evident. These results demonstrate that the lamb foetal adrenal has a substantial enzymic capacity for glucocorticoid synthesis throughout at least the last third of gestation. In conjunction with the observations of others, these experiments support the hypothesis that during this period of gestation the lamb foetal adrenal is actively synthesizing glucocorticoids in a manner which is similar to the lamb at term and the adult sheep.
N. Kyprianou, J. C. Gingell and P. Davies
Androgen receptors in nuclei from human prostate carcinomas were characterized on the basis of their solubilization by, or resistance to, micrococcal nuclease. By this means, androgen receptors were assigned to three nuclear categories: those associated with nuclease-resistant structures, those associated with chromatin and those apparently uncommitted by association with either of these. Prostate carcinoma nuclei contained high concentrations (57–82% of total nuclear content) of nuclease-resistant androgen receptors. This was a different pattern from that observed previously for benign hypertrophic prostate epithelial nuclei which contained a variable high proportion of uncommitted androgen receptors. The differences could not be attributed to differential losses to cytosol, or to loss of functionality, as determined in vitro. The differences in distribution could reflect different responses of diseased cells to androgens, or the intervention of other factors more relevant to the disease process.
J. Endocr. (1987) 112, 161–169
C. T. M. DAVIES and J. D. FEW
MRC Environmental Physiology Unit, London School of Hygiene and Tropical Medicine, Keppel Street, London, WC1E 7HT
(Received 8 April 1976)
Reports on the changes in plasma cortisol level induced by exercise are uncommon, but contradictory. We have previously shown that exercise for 1 h, only leads to a rise in plasma cortisol concentration if the work load exceeds about 60% of the subject's maximal aerobic power (V̄O2, max); that is if his oxygen consumption exceeds 60% of the maximum of which he is capable (Davies & Few, 1973). We have now obtained further evidence of the importance of relative work load (% V̄O2, max) in eliciting an adrenocortical response to exercise, by comparing the changes in plasma cortisol at a given work load under normoxic and hypoxic conditions. The hypoxic condition was breathing 13% oxygen which was expected to reduce V̄O2, max by about 25% (Davies & Sargeant, 1974).
J. R. G. CHALLIS, I. J. DAVIES and K. J. RYAN
Pregnant rabbits were treated with indomethacin (8–10 mg/kg/day) or dexamethasone (1·2–1·8 mg/kg/day) during late gestation. The effects of these treatments on the concentrations of progesterone and prostaglandin F (PGF) in the peripheral plasma, and the outcome of gestation were studied. Treatment with indomethacin significantly prolonged the length of gestation (P < 0·01) compared with control, untreated animals. In these treated animals, the plasma progesterone levels declined at a similar time to that in control rabbits but the increase in systemic PGF normally seen during late pregnancy was reduced. Dexamethasone treatment reliably induced premature delivery within 3–6 days. The plasma progesterone concentration fell rapidly during the first 24 h of dexamethasone administration, but in no animal was this associated with a significant increase in the plasma levels of PGF.
These results are consistent with the suggestion that prostaglandins are involved in the normal initiation of parturition in the rabbit. They do not support the hypothesis that the effect of dexamethasone on the length of gestation is mediated through an increase in the production of prostaglandin F.
N. T. DAVIES, K. A. MUNDAY and B. J. PARSONS
A study was made of the effects of cyclic AMP, theophylline, cycloheximide, puromycin and actinomycin D on the stimulation by angiotensin of fluid transport by sacs of rat colon mucosa.
Cyclic AMP and theophylline, added together or separately, had no effect on fluid transport by colon sacs, suggesting that the stimulation of fluid transport after the application of angiotensin is not mediated through cyclic AMP. Cycloheximide and puromycin (used at concentrations which block colon protein synthesis by 50–90%) had no effect on fluid transport by control colon sacs, but completely blocked the stimulatory response of the colon to angiotensin. In contrast, actinomycin D (at a concentration which significantly inhibits RNA synthesis) did not affect fluid transport in control or angiotensin-stimulated colon sacs. The results are discussed in relation to the possibility that protein synthesis, at the stage of translation, is involved in the action of angiotensin on fluid transport by the colon.
G. C. CASHMORE, C. T. M. DAVIES and J. D. FEW
MRC Environmental Physiology Unit, London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT
(Received 10 September 1976)
Exercise for 1 h, at work loads exceeding about 60% of a subject's maximum aerobic power (V̄O 2, max), generally leads to a rise in plasma cortisol concentration (Davies & Few, 1973). The observed rise in plasma cortisol level is the net effect of increases in both the rate of secretion, and the rate of removal from the plasma, of cortisol (Few, 1974). Occasionally exercise at work loads exceeding 70% V̄O 2, max fail to elicit a significant rise in plasma cortisol level. Such a result could be due either to a failure to increase the rate of cortisol secretion or to an unusually rapid rate of cortisol removal.
In an attempt to resolve this ambiguity we have analysed data from ten experiments on normal men who exercised for 1 h at
CAROL DAVIES, JOAN JACOBI, H. M. LLOYD and J. D. MEARES
The effects of 2-bromo-α-ergocryptine methanesulphonate on the response of the pituitary gland of the male rat to diethylstilboestrol dipropionate were studied by radioimmunoassay of prolactin and growth hormone and measurements of DNA synthesis. Given before diethylstilboestrol, 2-bromo-α-ergocryptine prevented the oestrogen-induced rise in serum prolactin and partly inhibited pituitary DNA synthesis. Given on days 4–6 of a 6-day period after a single dose of diethylstilboestrol, 2-bromo-α-ergocryptine rapidly increased pituitary prolactin concentration, diminished serum prolactin, reduced pituitary DNA synthesis and did not affect the growth hormone response to oestrogen.
S. J. MAIN, R. V. DAVIES and B. P. SETCHELL
Spermatogenesis in rats was interrupted by local X-irradiation, heat or ligation of the testicular efferent ducts. A significant and specific rise in the serum level of FSH occurred 5–8 days after ligation of the efferent ducts, reaching twice the value observed in shamoperated controls by 21 days after the operation. After the testes were heated to 43 °C for 30 min, the serum levels of both LH and FSH were raised within 3 days and remained so up to 50 days after treatment. After X-irradiation, no changes in the concentration of FSH were observed in the first 21 days after treatment, but the serum levels of both gonadotrophins were increased at 49 days. By comparing the relative increases in the concentrations of FSH and LH after germ cell damage with those occurring after castration, it was evident that testicular androgens could account for only part of the normal feedback control of FSH secretion; at least one third of the inhibition of FSH secretion appeared to be due to non-androgenic sources, presumably 'inhibin'.