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PubMed1993

Nuclear transfer and electrofusion in bovine in vitro-matured/in vitro-fertilized embryos: effect of media and electrical fusion parameters.

In this study, micromanipulation and electrofusion conditions for the cloning of in vitro-produced bovine embryos (here after termed IVM/IVF embryos) derived from in vitro-matured (IVM) and in vitro-fertilized (IVF) oocytes were established. The effect of DC field strength on the fusion rate was tested in a model system using pronuclear stage embryos in which a cytoplasmic vesicle was removed and reinserted. Efficient fusion (80%) was obtained by applying a pulse of 1.75 kV/cm for 40 microseconds. In vitro development of manipulated pronuclear stage embryos was as efficient as that of unmanipulated control embryos. Different fusion media were compared in the cloning procedure, using IVM oocytes as recipients and blastomeres from day 6 IVM/IVF donor embryos. Zimmermann cell fusion medium reduced the lysis of nuclear transfer embryos compared to F300 (5% vs. 25%). The effects of drugs disrupting the microfilaments and microtubuli were determined. Neither the addition of cytochalasin B (CCB) for 1 hr in the postfusion medium nor incubation of donor blastomeres with nocodazole had a significant effect on the fusion or cleavage rate of the nuclear transfer embryos. Additional experiments demonstrated that there was no difference in developmental potential between nuclear transfer embryos allowed to develop in vitro or in vivo and that the embryos gave a 15% pregnancy rate in recipient cattle.

Animals↗
PubMed2007

Suppression of connexin 43 and E-cadherin transcripts in in vitro derived bovine embryos following culture in vitro or in vivo in the homologous bovine oviduct.

In this study, a combination of RNAi and endoscopic transfer to the oviduct of synchronized heifers has been used to investigate the effect of suppression of Cx43 and E-cadherin on the development, mRNA and protein expression of bovine blastocysts cultured in vitro or in vivo. In vitro matured and fertilized bovine zygotes were randomly assigned to one of four groups namely: Connexin43 dsRNA-injected (n = 790), E-cadherin dsRNA-injected (n = 775), water-injected (n = 774), and noninjected controls (n = 652). Following 2 days in vitro culture, 4- and 8-cell stage embryos from each treatment group were used for culture in vitro or in vivo. About half of the 4-8-cell stage embryos from each treatment group were transferred to the oviduct of synchronized heifers, while the remainder were further cultured in vitro. Embryos from in vivo culture were flushed from recipients on the fourth day post transfer (= Day 7 post insemination). Blastocyst stage embryos from both culture systems were used for mRNA and protein expression analysis. Irrespective of treatment or culture conditions, microinjection resulted in a decline in the proportion of embryos reaching the blastocyst stage. Significantly, lower blastocyst development was observed in E-cadherin and water-injected embryos following in vivo culture compared to the noninjected controls, while intermediate results were obtained following injection with Cx43 dsRNA. Both mRNA and protein products of the target genes were suppressed but the efficiency of suppression of the target genes varied depending on the initial level of transcript abundance, which is known to be greatly affected by the culture environment.

Animals↗
PubMed2003

Pregnancies and births achieved from in vitro matured oocytes retrieved from poor responders undergoing stimulation in in vitro fertilization cycles.

OBJECTIVE: To describe pregnancies that resulted from in vitro matured oocytes derived from stimulated IVF cycles before cancellation owing to poor response of gonadotropins. DESIGN: Case report. University hospital. PATIENT(S): Eight patients who underwent in vitro maturation.Immature oocyte retrieval, in vitro maturation of immature oocytes, fertilization, and ET. Luteal support with progesterone and plvyeron was given. MAIN OUTCOME MEASURE(S): Pregnancy and live birth. RESULT(S): Three pregnancies (two live births and another ongoing) were achieved after immature oocyte retrieval, in vitro maturation, fertilization with ICSI, and ET. CONCLUSION(S): Immature oocyte retrieval from poor responders during stimulation, followed by in vitro maturation, may be an alternative before the cycle is canceled.

Adult↗
PubMed1987

Use of individual human follicles to compare oocyte in vitro fertilization to granulosa cell in vitro luteinization.

Granulosa-lutein (G-L) cells from individual follicles aspirated during cycles of in vitro fertilization-embryo transfer were examined after 3 and 6 days in culture. G-L cells from follicles that contained an oocyte that fertilized in vitro were compared with G-L cells from follicles that contained an oocyte that did not fertilize in vitro. Spent culture media was assayed for progesterone at days 3 and 6 of culture and luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor content of G-L cells was determined at day 6. G-L cell cultures from follicles that contained an oocyte that fertilized in vitro produced significantly more progesterone over 3 and 6 days of culture than those obtained from follicles in which the oocyte did not fertilize. Furthermore, LH/hCG receptor content after 6 days was significantly higher in G-L cells obtained from follicles with fertilized oocytes compared with follicles with unfertilized oocytes. Increased progesterone output and LH/hCG receptor acquisition demonstrate more maturation or "luteinization" by G-L cells aspirated from individual follicles that contain oocytes that fertilized in vitro.

Cells, Cultured↗
PubMed2002

A comparison of in vitro maturation and in vitro fertilization for women with polycystic ovaries.

OBJECTIVE: To establish the relative success of treatment by unstimulated in vitro maturation (IVM) of oocytes or stimulated in vitro fertilization (IVF) in women with polycystic ovaries undergoing assisted conception treatment. METHODS: The case-control study included 107 IVM and 107 IVF cycles matched for age and cause of infertility. In vitro maturation patients underwent transvaginal recovery of immature oocytes during an unstimulated cycle, in vitro oocyte maturation, and fertilization. Those in the IVF group underwent ovarian stimulation after pituitary suppression. Embryos were transferred in the same cycle in both groups. Main outcome measures included numbers of mature oocytes and embryos produced, and rates of implantation, pregnancy, live birth, and complications. RESULTS: In the IVM group after in vitro culture, 7.8 mature oocytes and 6.1 embryos were obtained per retrieval. With IVF, 12.0 mature oocytes (P <.01) and 9.3 embryos (P <.01) were obtained. The IVM pregnancy and live birth rates per retrieval were 26.2% and 15.9% compared with 38.3% and 26.2% for IVF (nonsignificant). The implantation rate of IVF-derived embryos was higher (17.1% versus 9.5%) than that for IVM (P <.01). There were 12 cases (11.2%) of moderate or severe ovarian hyperstimulation syndrome in IVF patients, compared with none in the IVM group (P <.01). CONCLUSION: Our results suggest that for women with polycystic ovaries who require assisted conception, IVM is a promising alternative to conventional IVF treatment.

Adult↗
PubMed2005

Microtubule and microfilament organization in immature, in vitro matured and in vitro fertilized prepubertal goat oocytes.

The aim of our study was to analyse the cytoskeletal organization of prepubertal goat oocytes. Microtubule and microfilament organization during in vitro maturation of prepubertal and adult goat oocytes and presumptive zygotes of in vitro matured-in vitro fertilized (IVM-IVF) prepubertal goat oocytes were analysed. Oocytes were matured in M-199 with hormones and serum and inseminated with frozen-thawed sermatozoa. Oocytes and presumptive zygotes were treated with anti-alpha-tubulin antibody and fluorescein isothiocyanate (FITC)-labelled goat anti-mouse antibody to stain the microtubules. Microfilaments were localized by means of phalloidin 5 microg/ml conjugated with fluorescein isothiocyanate (FITC-phalloidin). DNA was stained with propidium iodide. Stained oocytes were observed under a confocal laser scanning microscope. At the germinal vesicle nuclear stage, microfilaments were distributed at the cortex of the oocytes. After in vitro maturation, 91.7% of metaphase II (MII) oocytes from adult goats displayed microfilaments in the cortex and within the polar body and were characterized by the presence of a microfilament thickening at the cortical region over the meiotic spindle. In prepubertal goat MII oocytes only 5.7% of oocytes displayed microfilaments at the cortex and within the polar body. After insemination, most of the zygotes displayed microfilaments distributed at the cortex. An undefined microtubular network was observed in adult and prepubertal goat oocytes at the germinal vesicle stage. After in vitro maturation, 100% of MII oocytes from adult goats displayed microtubules on the meiotic spindle and within the polar body. This pattern of distribution was observed in 71.6% of prepubertal goat oocytes. Undefined microtubule networks were present in most of the zygotes analysed. In conclusion, cytoskeletal differences were found between prepubertal and adult goat MII oocytes. Furthermore, most of the zygotes from IVM-IVF prepubertal goat oocytes displayed cytoskeletal anomalies.

Actin Cytoskeleton↗
PubMed2002

Effects of serum-free culture media on in vitro development of domestic cat embryos following in vitro maturation and fertilization.

This study was conducted to determine the adequate medium for a serum-free culture system of domestic cat embryos produced by in vitro maturation (IVM) and fertilization (IVF). Cumulusoocyte complexes recovered from cat ovaries were matured in vitro for 24 h, and then inseminated in vitro for 12 h. After insemination, the oocytes were cultured in five media [Ham's F10, Waymouth 752/1 (Waymouth), TCM199, modified Earle's balanced salt solution (MK-1) and CR1aa], each of which contained 0.4% bovine serum albumin. There were no significant differences among the rates of fertilization of oocytes cultured in five media following IVF. The rate of oocytes/embryos developed to at least the morula stage was significantly lower (p < 0.05) in Waymouth than in MK-1, TCM199 and CR1aa. Moreover, none of the embryos cultured in Ham's F10 and Waymouth developed to the blastocyst stage. There were no differences among the rates of development to the blastocyst stage of oocytes/embryos cultured in MK-1, TCM199 and CR1aa. These results indicate that the type of serum-free medium has a major impact on in vitro development of domestic cat embryos derived from IVM/IVF, and MK-1, TCM199 and CR1aa media are suitable for in vitro culture of cat embryos in a serum-free culture system.

Animals↗
PubMed2005

In Vitro and in vivo developmental competence of dromedary (Camelus dromedarius) embryos produced in vitro using two culture systems (mKSOMaa and oviductal cells).

Development competence and pregnancy rate of in vitro-produced (IVP) dromedary embryos were studied in two culture systems: (i) semi-defined modified medium (mKSOMaa) and (ii) co-culture using camel epithelial oviducal cells. Five hundred and three cumulus-oocytes complexes (COCs) were selected, allowed to mature, fertilized and cultured in vitro (38.5 degrees C; 5% CO2, maximum humidity > 95%, with concentration of oxygen of 5% for semi-defined medium and 20% for co-culture cells). Maturation was accomplished by incubation in TCM-199 medium supplemented with 10% heat-treated foetal calf serum (FCS), 10 ng/ml epidermal growth factor, 1 microg/ml follicle-stimulating hormone, 1 microg/ml oestradiol and 500 microM cysteamine for 30 h. In vitro fertilization (IVF) was performed using fresh semen (0.5 x 10(6) spermatozoa/ml in modified TALP solution). Fertilized COCs were denuded by vortexing, then cultured in either mKSOMaa (10% heat-treated FCS was added 24 h post-IVF), under 5% O2 and 90% N2 (group 1; n = 249) or with dromedary epithelial oviducal cell monolayers in TCM-199 with 10% heat-treated FCS under 20% O2 (group 2; n = 254). The rate of cleavage was significant higher (p < 0.05) for group 1 (63%, 156/249) than for group 2 (51%, 130/254). No significant difference was found between the two groups in the rate of development to blastocyst (21% vs 16.5%) and their hatchability (21% vs 14%). Pregnancy rates were similar for the first 60 days. However, all pregnancies were lost after 60 days with the exception of two of six (33%) from recipients of hatched blastocysts from group 1. We conclude that both systems support in vitro production of dromedary embryos by in vitro maturation (IVM)/IVF of oocytes. However, embryos obtained by culture in the semi-defined medium (mKSOMaa) appear to have a better in vivo development ability.

Animals↗
PubMed1989

Differential effects of thyrotropin-releasing hormone on in vitro release of in vivo or in vitro newly synthesized and mature prolactin by lactating rat adenohypophyses. Further evidence for a sequential pattern of hormone release.

We studied the basal and thyrotropin-releasing hormone (TRH)-stimulated in vitro release of newly synthesized and mature prolactin (PRL) by lactating rat pituitary fragments. Newly synthesized PRL was defined as that resulting from either in vivo pulse labelling with [3H]-leucine (injected i.v. 10 min before removing the pituitary glands for in vitro incubation); or in vitro labelled by a 5-min preincubation period of adenohypophyseal fragments. Mature PRL was defined as that labelled in vivo 8 h before incubation. Medium PRL was quantified by polyacrylamide-gel-electrophoresis densitometric and liquid scintillation techniques. Under basal conditions, both total (unlabelled) and 8-hour labelled (mature) PRLs showed an in vitro release pattern characterized by an initial period of faster and higher secretion that lasted for 30-60 min followed by a lower secretion rate that extended from 60 to 240 min of incubation. Secretion of newly synthesized PRLs was detected since the first 30 min, but did not reach maximum levels until 90-120 min of incubation. Accordingly, PRL release during the first 30-60 min of incubation consisted primarily of mature PRL, whereas secretion during the rest of incubation included the release of newly synthesized hormone. These results confirm previous data on the sequential, rather than preferential, release of different age PRLs. TRH (0.35 microM) stimulated (about 30% above control) the release of both total and mature PRLs. No effect could be detected upon the release of in vivo labelled new PRL, while the same dose of TRH strongly stimulated (about 100% above control) the release of in vitro labelled new PRL.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1976

A simplified in vitro classification for prognosis in adult acute leukemia: the application of in vitro results in remission-predictive models.

Previous classification in vitro of adult acute leukemia incorporating morphology has been complex and difficult to understand. We have devised a simplified classification based solely on leuekemic proliferation in vitro. Seventy-six patients with adult acute leukemia previously untreated were included in this study and received identical chemotherapy. Three groups were recognized. The complete remission rate was 76% in the 21 patients with no leukemic growth in vitro (Group 1), 75% in 36 patients with leukemic cell growth but aggregates of 20 cells or less (Group 2), and only 21% in the 15 patients with aggregates of greater than 20 (Group 3). There was a highly significant difference in complete remission rates between Group 3 and the other two groups (p less than 0.001). Linear logistic regression analysis demonstrated the independence of the growth in vitro from other prognostic variables. A predictive model utilizing the in vitro result more accurately predicted for remission, both retrospectively and prospectively, than a model constructed with presently known prognostic parameters. The cause of death in failures suggested that this system detects resistance to the chemotherapy.

Acute Disease↗
PubMed1991

Studies of the proliferation and differentiation of immature myeloid cells in vitro: 4: Preculture proto-oncogene expression and the behaviour of myeloid leukemia cells in vitro.

Studies were conducted to determine the relationship between the pretherapy characteristics of leukemia cells and their behaviour during culture in vitro. Leukemia cells which proliferated well in vitro also proliferated well in vivo. Cells which manifested myeloid or monocytic differentiation in vivo tended to manifest differentiation along these lines in vitro. Cells which manifested high levels of expression of c-fms, c-fes, or triose phosphate isomerase prior to culture were likely to differentiate in vitro, with high levels of c-fes expression being related to myeloid maturation. These observations suggest that differentiation at the molecular level prior to culture is a requisite for leukemia cell differentiation in vitro. The same may be true for differentiation in vivo under the influence of exogenously administered agents such as cytotoxic chemotherapy or recombinant growth factors.

Adult↗
PubMed1994

In vitro-in vivo correlation of a modified-release oral form of ketotifen: in vitro dissolution rate specification.

The dissolution rate profile of a new modified-release (MR) oral tablet of ketotifen (Zaditen SRO tablet, Sandoz Ltd.) was determined under different conditions (pH, rpm, paddle or basket) with the U.S.P. apparatus. Three different variants of MR tablets were tested. In addition, the in vivo bioavailabilities of these MR tablets were evaluated after a single-dose administration under different conditions (fasting state, with food in morning and/or evening). Several possibilities were evaluated to obtain a correlation between in vitro and in vivo data of the three MR tablets. An excellent linear correlation (r = 0.997) was obtained between the cumulative dissolved percent in vitro and the cumulative absorbed percent in vivo at each time under certain conditions. This was obtained in vitro with the dissolution rate performed in distilled water (37 degrees C) with the U.S.P. apparatus 2 (rotating paddle) and in vivo after a single-dose administration in the morning, fasting state. On the basis of this correlation, of the in vitro dissolution rate for a given variant, and of a simple method of calculation, a reliable prediction of the plasma concentrations obtained following a single dose or at steady state was found. The reliability of this prediction was validated from variants of MR tablet presenting different in vitro dissolution rate profiles and with an upscaled batch which was tested in vivo. This result allows the specifications (upper and lower limits) of the dissolution rate for the MR tablet to be defined and ensures good in vivo characteristics for the different batches of Zaditen SRO tablets during manufacture.

Adult↗
PubMedDate not supplied

Perspectives of in vitro dissolution tests in establishing in vivo/in vitro correlations.

Perspectives of in vitro dissolution tests in establishing an in vivo/in vitro correlation are considered at three different levels. The first involves the selection of a drug product, or suitable batch(es), for the correlation study. This requires evaluation of the biopharmaceutical properties of the proposed drug from a profile compiled from a set of dissolution tests under different experimental conditions. These characteristics are needed for properly designing the in vivo study and are also referred to when only a poor correlation is obtained. The second is to define the specific in vitro test system either prospectively, by assessing plausibility of in vitro results, or retrospectively, after interpretation of in vivo data. This distinct test system has to be validated both physically and analytically. The third aspect of dissolution testing for correlations is to provide sound data and derived parameters in consideration of statistical aspects (variability) and of a sufficient number of suitable sampling intervals. In vitro models proposed for the special study of the simulation of food effects on bioavailability are discussed but concluded to be as yet not satisfactory for general application.

Animals↗
PubMed1996

The effect of in vivo and in vitro irradiation (25 Gy) on the subsequent in vitro growth of satellite cells.

The effect of in vivo and in vitro irradiation on subsequent satellite cell growth, in vitro, was investigated to ascertain the ability of a 25 Gy dose to inhibit satellite cell proliferation. Satellite cells were isolated from the left (irradiated) and right (non-irradiated) Pectoralis thoracicus of two-week-old tom turkeys 16 h (n=3) and seven weeks (n=2) after the left Pectoralis thoracicus had been irradiated (25 Gy). Satellite cells isolated from the irradiated and non-irradiated muscles exhibited similar (P>0.10) in vitro proliferation indicating that a population of satellite cells survived an in vivo dose of 25 Gy. In additional experiments, satellite cell cultures derived from tom turkey Pectoralis thoracicus were irradiated (25 Gy) in vitro. The number of satellite cells did not (P>0.05) increase in irradiated cultures for 134 h following irradiation, while satellite cells in non-irradiated cultures proliferated (P<0.05) over this time. At later time periods, satellite cell number increased (P<0.05) in irradiated cultures indicating that a population of satellite cells survived irradiation. The results of these in vitro experiments suggest that a 25 Gy dose of irradiation does not abolish satellite cell divisions in the turkey Pectoralis thoracicus.

Animals↗
PubMed1995

Human lymphocytes incubated in vitro share multiple characteristics with geriatric-derived lymphocytes: a potential in vitro model for aging?

Aging involves a complicated set of parallel reactions that result in multiple cellular and organismic changes and may eventuate in chronic illness. In the immune system, several alterations that correlate with age have been established. In the present study, we report the results of incubating lymphocytes in vitro in whole blood and, employing measures known to be age-dependent, compare these cells 'aged' in vitro with cells from geriatric patients aged in vivo. Cells from blood aged in vivo and incubated in vitro share a number of common characteristics that include decreased growth capacity, shifted growth patterns, increased suppression by adherent cells, decrease in CD5 surface antigen, similar responses to addition of exogenous IL-1, IL-2, PGE2, or indomethacin, and similar production of PGE2. Differences found between in vivo aging and in vitro incubation are IL-2 plasma levels and IL-2 production by activated cells monitored in conditioned minimal medium. Based on these observations, this in vitro system provides a simple method to generate cells that exhibit a very significant subset, but not all, of the characteristics associated with in vivo aging in lymphocytes.

Adult↗
PubMed1984

The in vitro micronucleus assay for detection of cytogenetic effects induced by mutagen-carcinogens: comparison with the in vitro sister-chromatid exchange assay.

The sensitivity of a cytogenetic assay, as expressed by the in vitro induction of micronuclei (MN), was compared to the in vitro induction of sister-chromatid exchanges (SCEs). Chinese hamster lung (V79) cells were exposed to 3 known alkylating agents: methyl methanesulphonate (MMS), ethyl methanesulphonate (EMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and to 5 newly synthesized naphthofurans: 2-nitro-7-methoxynaphtho[2,1-b]furan (A), 2-nitro-8-methoxynaphtho[2,1-b]furan (B), 2-nitronaphtho[2,1-b]furan (C), 2-nitro-7-bromonaphtho[2,1-b]furan (D) and 7-methoxynaphtho[2,1-b]furan (E). The induction of MN only was also analysed after exposure of the cells to 4 alcohols: ethanol, methanol, butanol and propanol. The lowest dose at which a significant effect could be observed was determined. In both assays, MNNG, MMS and EMS were equally active with the following order of potency: MNNG greater than MMS greater than EMS, the latter being a very weak inducer of MN and SCE. Compounds A and B were also very effective in both assays. Compound C was a more active inducer of SCE than MN. Compounds D and E were not active in either assay. None of the 4 alcohols induced MN. Our results are compared with the previously published data on in vitro and in vivo induction of SCE and MN. We conclude that the MN in vitro assay which detects clastogens as well as agents affecting the spindle apparatus, is a good indicator of genotoxicity, though slightly less sensitive than the in vitro SCE test. It could provide a rapid, simple and inexpensive complementary short-term test for the evaluation of potentially mutagenic chemicals.

Alcohols↗
PubMed1997

Comparative evaluation of the in vitro micronucleus test and the in vitro chromosome aberration test: industrial experience.

Because of its rapidness, simplicity and potential for automation, the measurement of micronucleated cells in vivo is not only equivalent to the analysis of chromosome aberrations, but often even preferred within routine genotoxicity testing. In order to evaluate the correlation between the in vitro micronucleus assay (MNT) and the in vitro chromosome aberration test (CA), we collected data from four pharmaceutical companies obtained either in Chinese hamster cell lines (CHO-K5, CHO-K1, V79) or in human peripheral blood lymphocytes. Among the 57 compounds included in this comparison, 45 compounds gave rise to concordant results in both assays (26 compounds negative in both assays; 19 compounds positive in both assays). The high percentage of concordance, i.e. about 79% is very promising and can be even increased to about 88% by omitting the 3 aneugenic compounds and 2 compounds inducing endoreduplicated chromosomes which were found positive only in the in vitro MNT. The results are remarkable in particular considering that most of the compounds evaluated are 'standard' pharmaceutical compounds and thus are at most weak inducers of chromosome damage. Our comparison strongly supports that the in vitro micronucleus test is a suitable alternative to the in vitro chromosome aberration assay. Moreover, the MNT has the potential of not only detecting clastogens but additionally aneuploidy inducing chemicals.

Animals↗
PubMed1992

Growth hormone-releasing factor analogs with hydrophobic residues at position 19. Effects on growth hormone releasing activity in vitro and in vivo, stability in blood plasma in vitro, and secondary structure.

To test the hypothesis that replacing Ala19 in growth hormone-releasing factor (GRF) with more hydrophobic residues will increase growth hormone releasing activity, four GRF analogs were prepared and tested. The molecules were made by substituting Val, Ile, or Leu at position 19 of [Thr2,Ala15,Leu27]bGRF(1-29)NH2. The compounds were evaluated for growth hormone (GH) releasing activity in vitro (rat anterior pituitary cells) and in vivo (steers). Additionally, their half-life in vitro was determined in bovine plasma, and their secondary structure was examined by circular dichroism. In pituitary cells, peptides with substitutions at position 19 had the following potencies: Ala (native), 0.37; Val, 1.16; Ile, 0.37; Leu, 0.043. When assayed in steers as a single iv bolus, over a 2-h period, the compounds gave the following integrated GH response: Ala, 2.75; Val, 2.67; Ile, 2.57; Leu, 1.55. Only the Leu analog was statistically different from the other three (p = 0.05). In bovine plasma, the half-lives (hours) were as follows: Ala, 4.9; Val, 6.6; Ile, 12.3; Leu, 14.7. In phosphate buffer the compounds were calculated to have the following percent helical content: Ala, 26; Val, 21; Ile, 27; Leu, 32. For these analogs, helicity in aqueous buffer is inversely related to their in vitro activity. Using a linear multiple regression model, the plasma half-life of the analogs positively correlated (r2 = 0.999) with both the hydrophobicity of the residue at position 19 and the helicity of the analog. Although the Val analog had both increased inherent activity and increased plasma stability in vitro compared to the Ala analog, in this study we were unable to demonstrate an increase in activity in vivo. The in vivo GH releasing activity of the analogs was not simply related to a combination of their intrinsic GH releasing activity and their in vitro plasma half-life. This suggests that in vivo additional factors are moderating the expression of activity.

Amino Acid Sequence↗