Respiratory metabolism of developing eggs of Schistocerca gregaria has been individually monitored by means of scanning microrespirography. The freshly oviposited eggs consumed 7 nl of O2 /min./egg (50 µl O2/g/h) while the pharate 1st instar larvae shortly before hatching consumed 141 nl of O2/min./egg (550 µl O2/g/h), which shows 20-fold metabolic increase during the egg stage. The output of CO2 was also regular, without discontinuous bursts throughout the whole embryonic development. The amounts of CO2 produced were constantly close to R.Q. ratio of 0.7, suggesting that lipid was the main energetic source. The vermiform, pharate 1st instar larvae emerging from the eggs exhibited very high respiratory rates (up to 3,000 µl O2/g/h). During initial phases of the egg stage, O2 consumption steadily increased until day 6, which was associated with katatrepsis or blastokinesis stage of the embryo (61 nl of O2/egg/min. = 240 µl O2/g/h). Since blastokinesis, respiratory metabolism of the egg remained constant or decreased steadily until day 10, when it rose sharply again towards hatching. The temporary metabolic depression was closely correlated with endogenous peak in ecdysteroid concentration within the embryo. These results corroborate validity of the reciprocal, high ecdysteroid - low metabolism rule previously known from insect metamorphosis. They extend its application into the period of embryogenesis. Practical implications of certain physiological, morphological and evolutionary consequences of these findings are discussed with special emphasis on the connecting links between embryogenesis and metamorphosis.
A comparative study of mitotic activities and haemolymph ecdysteroid levels was performed in the phasmid Clitumnus extradentatus. Temporal correlation was found between increases in mitotic frequency in mandibular and general epidermis, and variations of ecdysteroid levels in the haemolymph of the insects. Whereas, mitotic waves occurring in the fat body cells or in the basal cells of the midgut did not appear to be strictly correlated with these hormonal variations. During the fourth larval instar of this phasma; an accurate study of mitotic figures, monitored from histological sections, indicated a time-lag in their stimulation according to the studied area, with a peak on day 2 in the mandible tips, on day 5 in the mandible bases and on day 7 in the head capsule, thorax and abdomen epidermis: namely a five-day delay with respect to the 12 days of the fourth instar. Simultaneously, the evolution of ecdysteroid levels in the haemolymph showed three increases of different importance. Each hormonal increase occurred 24 h before the triggering of each increase in the mitotic activity, whereas a fourth and very high peak, occurring on day 8, corresponded to the sudden fall in the number of epidermal mitoses.
Polyhydroxylated derivatives of 6-keto,7-dehydrocholesterol (ecdysteroids) are common constituents of various plants.
In 1965, they were accidentally discovered in the search for the insect moulting hormone. These biologically important natural
compounds are neither insect hormones nor inducers of insect ecdysis. Due to their strong anabolic, vitamin D-like effects in insects, domestic animals and humans, I propose the use of the arbitrary term vitamin D1
. The present paper describes the effects
of vitamin D1
on the growth and regeneration of excised epidermal cells of the tobacco hornworm, Manduca sexta (Sphingidae).
The periods of programmed cell death and cell proliferation (histolysis and histogenesis, respectively) exactly coincide in insects
with endogenous peaks of increased concentration of vitamin D1
. Epidermal cells communicate with each other, creating a mutually integrated tissue, connected by mechanical, chemical, electrical, ionic or other so far incompletely known factors. After natural
cell death, or after the artifi cial removal of some epidermal cells, the neighbouring cells that lose communication integrity, begin
to divide mitotically to replace the disconnected part. Cell divisions are arrested as soon as the integrity of the living tissue is
established. During insect ontogeny, the application of juvenile hormone causes regenerating epidermal cells to repeat the previous morphogenetic programme (i.e., development of patches of larval tissue on the body of a pupa, or metathetely). Conversely,
the application of vitamin D1
(20-hydroxyecdysone) caused the regenerating cells to prematurely execute a future morphogenetic
programme (i.e., development of patches of pupal tissue on the body of a larva, or prothetely). Among the key features of insect
regeneration, is the arrest of cell divisions when tissues resume living cell-to-cell integrity. This prevents the formation of aberrant groups of cells, or tumours. It is well established that the main physiological systems of insects (e.g., circulatory, respiratory,
neuro-endocrine) are structurally and functionally similar to corresponding systems in humans. Thus the basic principles of cell
regeneration and the role of vitamin D1
in insects may also be valid for humans. The common vitamins D2
(ergocalciferol) or D3
(cholecalciferol), are exclusively lipid soluble secosterols, which require activation by UV irradiation and hydroxylation in the liver.
By contrast, the neglected vitamin D1
is a natural derivative of polyhydroxylated 7-dehydrocholesterol of predominantly plant origin, which is both partly a water and partly a lipid soluble vitamin. It neither requires UV irradiation, nor hydroxylation due to 6 or
7 already built-in hydroxylic groups. Like other vitamins, it enters insect or human bodies in plant food or is produced by intestinal
symbionts. Vitamin D1
causes strong anabolic, vitamin D-like effects in domestic animals and in humans. I am convinced that
avitaminosis associated with a defi ciency of vitamin D1 in human blood may be responsible for certain hitherto incurable human
diseases, especially those related to impaired nerve functions and somatic growth, aberrant cell regeneration or formation of
malignant tumours.