Considerations for Measurement of Embryonic Organ Growth

Hemeoxygenase-2 (HO-2) is an antioxidant enzyme that can modulate recombinant maxi-K+ channels and has been proposed to be the acute O2 sensor in the carotid body (CB). We have tested the physiological contribution of this enzyme to O2 sensing using HO-2 null mice. HO-2 deficiency leads to a CB phenotype characterized by organ growth and alteration in the expression of stress-dependent genes, including the maxi-K+ channel α-subunit. However, sensitivity to hypoxia of CB is remarkably similar in HO-2 null animals and their control littermates. Moreover, the response to hypoxia in mouse and rat CB cells was maintained after blockade of maxi-K+ channels with iberiotoxin. Hypoxia responsiveness of the adrenal medulla (AM) (another acutely responding O2-sensitive organ) was also unaltered by HO-2 deficiency. Our data suggest that redox disregulation resulting from HO-2 deficiency affects maxi-K+ channel gene expression but it does not alter the intrinsic O2 sensitivity of CB or AM cells. Therefore, HO-2 is not a universally used acute O2 sensor.

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On the Nature of Hereditary Size Limitation

Journal of Experimental Biology ◽

10.1242/jeb.6.4.311 ◽

1929 ◽

Vol 6 (4) ◽

pp. 311-324

Author(s):

R. CUMMING ROBB

Keyword(s):

Body Weight ◽

Body Mass ◽

Physical Significance ◽

Body Parts ◽

Total Body Mass ◽

Organ Growth ◽

Submaxillary Glands ◽

Size Limitation ◽

Similar Association ◽

Total Body

1. Throughout post-natal life the relative weights of the pituitary body, thyroid, thymus and adrenals in the rabbit may be expressed by the equation y = axk + c. 2. A similar association is indicated in the rat for the weights of eyeballs, liver, pancreas, hypophysis, thyroid, adrenals, submaxillary glands, kidney and fresh skeleton (data from Donaldson, 1924). 3. In giant and pigmy rabbits, the ultimate proportions of body parts are not the same, but (for any given body weight) corresponding tissues in the two groups tend to exhibit an identical relation to total body mass. 4. The adrenals and testes of the Polish rabbits are relatively much larger than those of the Flemish. But in each case the growth of the adrenal approximates to a constant power function of body weight. Moreover, in these two groups and in their hybrids, the growth of the testes adheres to a simple association with adrenal weight identical for each. 5. These data suggest the generalisation that in a growing organism the magnitude of any part tends to be a specific function of the total body mass or of some portion so related to the whole. 6. These associations may be explained by surmising that each tissue is in equilibrium with the internal milieu with regard to the distribution of nutrient growth essentials; that in each case the equilibrium point would be determined by the nature of the cell and after differentiation would tend to remain constant; and that the relative enlargement of each tissue is limited by the excess of the equilibrium value over the katabolic expenditure. 7. According to the above hypothesis of organ growth, the equation y = axk + c may possess a physical significance. Eight types of growth relationships may thus exist, differing because of the apparent inactivity of one or more constants in this equation.

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