|Budget Amount *help
¥2,400,000 (Direct Cost : ¥2,400,000)
Fiscal Year 1995 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1994 : ¥1,700,000 (Direct Cost : ¥1,700,000)
We successfully developed endothelin (ET)-1 gene knckout mice and used them in the following experiment. 1) We were able to obtain stable recordings of the mice's blood pressure and heart rate, without any restriction nor anesthesia, for more than 2 hours. Obtained large quantity of data was handled with an aid of a computer. 2) By body plethysmography, we measured ventilation movement and its reflex change to hypoxia or hypercapnia in mature and new born conscious mice. 3) We recorded phrenic nerve discharges in urethane-anesthetized adult mice and measured their reflex change in response to hypoxia or hypercapnia. 4) Finally, we tested whether power spectral analysis of blood pressure fluctuations could be used in the mice as an evaluation method of autonomic nerve function.
As a result, homozygotes that completely lost ET-1 gene died soon after birth by abnormal formation of craniofacial tissues. On the other hand, heterozygotes of which plasma concentration of ET-1 was about half of
the normal mice showed significantly higher blood pressure than in the controls. In ET-1 deficient heterozygous mice, arterial pO_2 was significantly lower, pCO_2 tended to be higher and pH tended to be lower than in wild-type littermates. When these conscious mice breathed room air, respiratory minute volume and rate were not different between the two groups, although reflex increase to hypoxia or hypercapnia was significantly attenuated in ET-1^<+/-> heterozygotes. Since impaired reflex responses were also evident by recording phrenic nerve discharges, the cause of ventilatory impairment lay, at least in part, in the nervous system. Furthermore, in homozygotes that were delivered by cesarian sections and tracheotomized, reflex increase in ventilation was severely attenuated. Thus ET-1 plays a pivotal role in reflex control of respiration. Abnormality of breathing regulation in ET-1 deficient mice may account for the elevated blood pressure. In fact, similar cardiorespiratory abnormality was suggested by power spectrum analysis of blood pressure fluctuations.
In summary, ET-1 participates in development and cardiorespiratory regulation in mice. This is an important and new finding and widens the suggested notion that ET-1 is not a mere vasoconstrictor but a playr of a variety of physiological roles. Moreover, it becomes clear that many of the techniques to study autonomic nervous function in the whole animal can be used in such a small animal as mouse with some modifications. Less