Rate of oxidative and glycolytic metabolism in the guinea-pig oviduct in relation to contractility and hormonal cycle

Chronic fetal hypoxia disrupts the peri-conceptual environment in next-generation adult female rats

KEY POINTS

Exposure to chronic hypoxia during gestation influences long-term health and development, including reproductive capacity, across generations. If the peri-conceptual environment in the developing oviduct is affected by gestational hypoxia, then this could have implications for later fertility and the health of future generations. In the present study, we show that the oviducts of female rats exposed to chronic hypoxia in utero have reduced telomere length, decreased mitochondrial DNA biogenesis and increased oxidative stress The results of the present study show that exposure to chronic gestational hypoxia leads to accelerated ageing of the oviduct in early adulthood and they help us understand how exposure to hypoxia during development could influence reproductive health across generations.

ABSTRACT

Exposure to chronic hypoxia during fetal development has important effects on immediate and long-term outcomes in offspring. Adverse impacts in adult offspring include impairment of cardiovascular function, metabolic derangement and accelerated ovarian ageing. However, it is not known whether other aspects of the female reproductive system may be similarly affected. In the present study, we examined the impact of chronic gestational hypoxia on the developing oviduct. Wistar rat dams were randomized to either normoxia (21%) or hypoxia (13%) from day 6 post-mating until delivery. Post-delivery female offspring were maintained in normoxia until 4 months of age. Oviductal gene expression was assayed at the RNA (quantitative RT-PCR) and protein (western blotting) levels. Oviductal telomere length was assayed using Southern blotting. Oviductal telomere length was reduced in the gestational hypoxia-exposed animals compared to normoxic controls (P < 0.01). This was associated with a specific post-transcriptional reduction in the KU70 subunit of DNA-pk in the gestational hypoxia-exposed group (P < 0.05). Gestational hypoxia-exposed oviducts also showed evidence of decreased mitochondrial DNA biogenesis, reduced mtDNA copy number (P < 0.05) and reduced gene expression of Tfam (P < 0.05) and Pgc1α (P < 0.05). In the hypoxia-exposed oviducts, there was upregulation of mitochondrial-specific anti-oxidant defence enzymes (MnSOD; P < 0.01). Exposure to chronic gestational hypoxia leads to accelerated ageing of the oviduct in adulthood. The oviduct plays a central role in early development as the site of gamete transport, syngamy, and early development; hence, accelerated ageing of the oviductal environment could have important implications for fertility and the health of future generations.

Effects of extracellular K+ and Ca2+ on membrane potential, contraction and 86Rb+ efflux in guinea-pig mesotubarium

The effects of varying extracellular concentrations of K+ and Ca2+ [K+]o and [Ca2+]o on force development and membrane potential were investigated in the guinea-pig mesotubarium. At [K+]o up to 40 mM, spontaneous action potentials were present, while higher [K+]o gave sustained contractures at a stable membrane potential (-24 to -12 mV for [K+]o from 60 to 120 mM). Tension decreased successively with increasing [K+]o from 30 to 120 mM. The relaxing potency of the dihydropyridine Ca2+ antagonist, felodipine, increased as the membrane was depolarized with increasing [K+]o and action potentials ceased. These results are compatible with the existence of Ca2+ channels showing voltage-dependent affinity with dihydrophyridines. Increasing [Ca2+]o from 2.5 to 10 mM caused membrane hyperpolarization by about 11 mV and was accompanied by a lower frequency of spontaneous contractions and a longer duration of the relaxation between contractions. 86Rb+ efflux measurements in 60 mM K+ in the absence and presence of felodipine revealed a Ca2(+)-dependent component of the voltage-activated efflux. In normal solution (5.9 mM K+), efflux in the presence of felodipine was similar to the minimal value during normal spontaneous activity. The results indicate regulation of the permeability of K+ channels by the intracellular Ca2+ concentration ([Ca2+]i) and suggest participation of such channels in the generation of the regularly occurring bursts of action potentials characteristic of spontaneous activity in the mesotubarium.

Spontaneous electrical and contractile activity correlated to 86Rb+ efflux in smooth muscle of guinea-pig mesotubarium

1. The spontaneous mechanical activity of guinea-pig mesotubarium consists of fused tetanic contractions lasting about 6 min, with a frequency of about four per hour. The muscle is completely relaxed between the contractions. Stretching the relaxed muscle elicits a contraction of the same appearance as the spontaneous ones. Comparison of preparations from oestrus (day 1 of the hormonal cycle), dioestrus (days 9-11) and prooestrus (days 14-15) showed no variation in the pattern of mechanical activity. 2. The resting membrane potential, measured by intracellular microelectrodes, did not differ with hormonal phase (prooestrus: -63.5 +/- 0.84 (n = 16); oestrus: -63.7 +/- 1.6 (n = 5); dioestrus: -61.6 +/- 0.77 (n = 17]. In most recordings a depolarization of a few millivolts occurred during the relaxation period (5-10 min), but in a few cells a more pronounced spontaneous depolarization of 10-15 mV was found. Ouabain (1 microM) caused depolarization by about 9 mV, both in pro- and dioestrus, leading to the initiation of maintained repetitive spiking. 3. Contraction is preceded by a depolarization lasting 10-30 s, and when a threshold is reached a train of slow waves and spikes is elicited. The frequency of slow waves and the number of spikes on each slow wave progressively decrease during the contraction, until spiking eventually ceases. 4. The spikes are resistant to tetrodotoxin (0.5 microM) and disappear in Ca2+-free medium, which also causes membrane depolarization. The duration of contractions increased with Ca2+ concentration in the range 1-5 mM. 5. The rate of 86Rb+ efflux, expressed as fractional release in 2 min intervals, showed a consistent variation during the contractile cycle in preparations with regular spontaneous activity. Relative to the value at the end of the relaxed period the efflux rate increased by about twofold during the contraction. From the beginning of the relaxed period after the contraction the efflux rate decreased by about 25% until the beginning of the next contraction. 6. It is concluded that the contractile activity in the mesotubarium, as opposed to that of the fallopian tube (Lydrup & Hellstrand, 1986a), is independent of the hormonal phase, including the period around ovulation. The mechanism for initiation of the trains of action potentials associated with spontaneous contractions may involve a gradual decrease of permeability of K+ channels or activity of the Na+-K+ pump during the relaxed period.